4. Maximum length of a SQL statement is 65480 characters;
4. Maximum length of a SQL statement is 65480 characters;
5. Database has more storage-related configuration parameters, see System Management.
5. Database has more storage-related configuration parameters, see System Management.
-Show current system parameters
-**Show current system parameters**
-```mysql
```mysql
SHOW VARIABLES;
SHOW VARIABLES;
```
```
- Use a database
Use/switch database
-Drop a database
-**Use a database**
Delete a database, all data tables included will be deleted. Please use with caution.
```mysql
USE db_name;
```
Use/switch database
- Modify database parameters
-**Drop a database**
```mysql
DROP DATABASE [IF EXISTS] db_name;
```
Delete a database, all data tables included will be deleted. Please use with caution.
-```mysql
-**Modify database parameters**
ALTER DATABASE db_name COMP 2;
```
COMP parameter modifies the database file compression flag bit, with the default value of 2 and the value range is [0, 2]. 0 means no compression, 1 means one-stage compression, and 2 means two-stage compression.
```mysql
ALTER DATABASE db_name COMP 2;
```
COMP parameter modifies the database file compression flag bit, with the default value of 2 and the value range is [0, 2]. 0 means no compression, 1 means one-stage compression, and 2 means two-stage compression.
```mysql
```mysql
ALTER DATABASE db_name REPLICA 2;
ALTER DATABASE db_name REPLICA 2;
```
```
REPLICA parameter refers to the number of replicas of the modified database, and the value range is [1, 3]. For use in a cluster, the number of replicas must be less than or equal to the number of DNODE.
- REPLICA parameter refers to the number of replicas of the modified database, and the value range is [1, 3]. For use in a cluster, the number of replicas must be less than or equal to the number of DNODE.
```mysql
ALTER DATABASE db_name KEEP 365;
```
The KEEP parameter refers to the number of days to save a modified data file. The default value is 3650, and the value range is [days, 365000]. It must be greater than or equal to the days parameter value.
```mysql
```mysql
ALTER DATABASE db_name KEEP 365;
ALTER DATABASE db_name QUORUM 2;
```
```
QUORUM parameter refers to the number of confirmations required for successful data writing, and the value range is [1, 3]. For asynchronous replication, quorum is set to 1, and the virtual node with master role can confirm it by itself. For synchronous replication, it needs to be at least 2 or greater. In principle, Quorum > = 1 and Quorum < = replica number, which is required when starting a synchronization module instance.
- The KEEP parameter refers to the number of days to save a modified data file. The default value is 3650, and the value range is [days, 365000]. It must be greater than or equal to the days parameter value.
```mysql
```mysql
ALTER DATABASE db_name QUORUM 2;
```
-
QUORUM parameter refers to the number of confirmations required for successful data writing, and the value range is [1, 3]. For asynchronous replication, quorum is set to 1, and the virtual node with master role can confirm it by itself. For synchronous replication, it needs to be at least 2 or greater. In principle, Quorum > = 1 and Quorum < = replica number, which is required when starting a synchronization module instance.
```mysql
ALTER DATABASE db_name BLOCKS 100;
ALTER DATABASE db_name BLOCKS 100;
```
```
BLOCKS parameter is the number of cache-sized memory blocks in each VNODE (TSDB), so the memory size used for a VNODE equals roughly (cache * blocks). Value range is [3,1000].
- BLOCKS parameter is the number of cache-sized memory blocks in each VNODE (TSDB), so the memory size used for a VNODE equals roughly (cache * blocks). Value range is [3,1000].
```mysql
```mysql
ALTER DATABASE db_name CACHELAST 0;
ALTER DATABASE db_name CACHELAST 0;
```
```
CACHELAST parameter controls whether last_row of the data subtable is cached in memory. The default value is 0, and the value range is [0, 1]. Where 0 means not enabled and 1 means enabled. (supported from version 2.0. 11)
- CACHELAST parameter controls whether last_row of the data subtable is cached in memory. The default value is 0, and the value range is [0, 1]. Where 0 means not enabled and 1 means enabled. (supported from version 2.0. 11)
**Tips**: After all the above parameters are modified, show databases can be used to confirm whether the modification is successful.
Tips: After all the above parameters are modified, show databases can be used to confirm whether the modification is successful.
3. The length of each row of the table cannot exceed 16k characters;
3. The length of each row of the table cannot exceed 16k characters;
4. Sub-table names can only consist of letters, numbers, and underscores, and cannot begin with numbers
4. Sub-table names can only consist of letters, numbers, and underscores, and cannot begin with numbers
5. 10)If the data type binary or nchar is used, the maximum number of bytes should be specified, such as binary (20), which means 20 bytes;
5. If the data type binary or nchar is used, the maximum number of bytes should be specified, such as binary (20), which means 20 bytes;
- Create a table via STable
-```mysql
-**Create a table via STable**
CREATE TABLE [IF NOT EXISTS] tb_name USING stb_name TAGS (tag_value1, ...);
```
Use a STable as template and assign tag values to create a data table.
```mysql
CREATE TABLE [IF NOT EXISTS] tb_name USING stb_name TAGS (tag_value1, ...);
```
Use a STable as template and assign tag values to create a data table.
-**Create a data table using STable as a template and specify a specific tags column**
-**Create a data table using STable as a template and specify a specific tags column**
-```mysql
```mysql
CREATE TABLE [IF NOT EXISTS] tb_name USING stb_name (tag_name1, ...) TAGS (tag_value1, ...);
CREATE TABLE [IF NOT EXISTS] tb_name USING stb_name (tag_name1, ...) TAGS (tag_value1, ...);
```
```
Using the specified STable as a template, specify the values of some tags columns to create a data table. (Unspecified tags columns are set to null values.)
Using the specified STable as a template, specify the values of some tags columns to create a data table. (Unspecified tags columns are set to null values.)
Note: This method has been supported since version 2.0. 17. In previous versions, tags columns were not allowed to be specified, but the values of all tags columns must be explicitly given.
Note: This method has been supported since version 2.0. 17. In previous versions, tags columns were not allowed to be specified, but the values of all tags columns must be explicitly given.
- Create tables in batches
-```mysql
CREATE TABLE [IF NOT EXISTS] tb_name1 USING stb_name TAGS (tag_value1, ...) tb_name2 USING stb_name TAGS (tag_value2, ...) ...;
```
Create a large number of data tables in batches faster. (Server side 2.0. 14 and above)
Note:
1. The method of batch creating tables requires that the data table must use STable as a template.
2. On the premise of not exceeding the length limit of SQL statements, it is suggested that the number of tables in a single statement should be controlled between 1000 and 3000, which will obtain an ideal speed of table building.
- Drop a table
- Show all data table information under the current database
Show all data table information under the current database.
-**Create tables in batches**
Note: Wildcard characters can be used to match names in like. The maximum length of this wildcard character string cannot exceed 24 bytes.
```mysql
CREATE TABLE [IF NOT EXISTS] tb_name1 USING stb_name TAGS (tag_value1, ...) tb_name2 USING stb_name TAGS (tag_value2, ...) ...;
```
Create a large number of data tables in batches faster. (Server side 2.0. 14 and above)
Note:
1. The method of batch creating tables requires that the data table must use STable as a template.
2. On the premise of not exceeding the length limit of SQL statements, it is suggested that the number of tables in a single statement should be controlled between 1000 and 3000, which will obtain an ideal speed of table building.
Wildcard matching: 1) '%' (percent sign) matches 0 to any number of characters; 2) '_' underscore matches one character.
-**Drop a table**
```mysql
DROP TABLE [IF EXISTS] tb_name;
```
-Modify display character width online
-**Show all data table information under the current database**
- Get schema information of a table
```mysql
SHOW TABLES [LIKE tb_name_wildcar];
```
Show all data table information under the current database.
Note: Wildcard characters can be used to match names in like. The maximum length of this wildcard character string cannot exceed 24 bytes.
Wildcard matching: 1) '%' (percent sign) matches 0 to any number of characters; 2) '_' underscore matches one character.
-Add a column to table
-**Modify display character width online**
-```mysql
```mysql
ALTER TABLE tb_name ADD COLUMN field_name data_type;
SET MAX_BINARY_DISPLAY_WIDTH <nn>;
```
```
Note:
-**Get schema information of a table**
```mysql
DESCRIBE tb_name;
```
1. The maximum number of columns is 1024 and the minimum number is 2;
-**Add a column to table**
2. The maximum length of a column name is 64;
- Drop a column in table
```mysql
ALTER TABLE tb_name ADD COLUMN field_name data_type;
```
Note:
1. The maximum number of columns is 1024 and the minimum number is 2;
2. The maximum length of a column name is 64;
-```mysql
-**Drop a column in table**
ALTER TABLE tb_name DROP COLUMN field_name;
```
If the table is created through a STable, the operation of table schema changing can only be carried out on the STable. Moreover, the schema changes for the STable take effect for all tables created through the schema. For tables that are not created through STables, you can modify the table schema directly.
```mysql
ALTER TABLE tb_name DROP COLUMN field_name;
```
If the table is created through a STable, the operation of table schema changing can only be carried out on the STable. Moreover, the schema changes for the STable take effect for all tables created through the schema. For tables that are not created through STables, you can modify the table schema directly.
Note: In 2.0. 15.0 and later versions, STABLE reserved words are supported. That is, in the instruction description later in this section, the three instructions of CREATE, DROP and ALTER need to write TABLE instead of STABLE in the old version as the reserved word.
Note: In 2.0. 15.0 and later versions, STABLE reserved words are supported. That is, in the instruction description later in this section, the three instructions of CREATE, DROP and ALTER need to write TABLE instead of STABLE in the old version as the reserved word.
- Create a STable
-**Create a STable**
Similiar to a standard table creation SQL, but you need to specify name and type of TAGS field.
Note:
1. Data types of TAGS column cannot be timestamp;
2. No duplicated TAGS column names;
3. Reversed word cannot be used as a TAGS column name;
4. The maximum number of TAGS is 128, and at least 1 TAG allowed, with a total length of no more than 16k characters.
Similiar to a standard table creation SQL, but you need to specify name and type of TAGS field.
Note:
1. Data types of TAGS column cannot be timestamp;
2. No duplicated TAGS column names;
3. Reversed word cannot be used as a TAGS column name;
4. The maximum number of TAGS is 128, and at least 1 TAG allowed, with a total length of no more than 16k characters.
-```mysql
-**Drop a STable**
DROP STABLE [IF EXISTS] stb_name;
```
Drop a STable automatically deletes all sub-tables created through the STable.
```mysql
DROP STABLE [IF EXISTS] stb_name;
```
Drop a STable automatically deletes all sub-tables created through the STable.
-Show all STable information under the current database
-**Show all STable information under the current database**
-```mysql
```mysql
SHOW STABLES [LIKE tb_name_wildcard];
SHOW STABLES [LIKE tb_name_wildcard];
```
```
View all STables under the current database and relevant information, including name, creation time, column number, tag number, number of tables created through the STable, etc.
View all STables under the current database and relevant information, including name, creation time, column number, tag number, number of tables created through the STable, etc.
-**Obtain schema information of a STable**
- Obtain schema information of a STable
```mysql
DESCRIBE stb_name;
```
-```mysql
-**Add column to STable**
DESCRIBE stb_name;
```
- Add column to STable
```mysql
ALTER STABLE stb_name ADD COLUMN field_name data_type;
```
-Drop column in STable
-**Drop column in STable**
-```mysql
```mysql
ALTER STABLE stb_name DROP COLUMN field_name;
ALTER STABLE stb_name DROP COLUMN field_name;
```
```
## <a class="anchor" id="tags"></a> TAG Management in STable
## <a class="anchor" id="tags"></a> TAG Management in STable
- Add a tag
-**Add a tag**
Add a new tag to the STable and specify a type of the new tag. The total number of tags cannot exceed 128 and the total length does not exceed 16K characters.
- Drop a tag
-```mysql
ALTER STABLE stb_name DROP TAG tag_name;
```
Delete a tag of STable. After deleting the tag, all sub-tables under the STable will also automatically delete the same tag.
- Modify a tag name
```mysql
ALTER STABLE stb_name ADD TAG new_tag_name tag_type;
```
Add a new tag to the STable and specify a type of the new tag. The total number of tags cannot exceed 128 and the total length does not exceed 16K characters.
-```mysql
-**Drop a tag**
ALTER STABLE stb_name CHANGE TAG old_tag_name new_tag_name;
```
Modify a tag name of STable. After modifying, all sub-tables under the STable will automatically update the new tag name.
```mysql
ALTER STABLE stb_name DROP TAG tag_name;
```
Delete a tag of STable. After deleting the tag, all sub-tables under the STable will also automatically delete the same tag.
-Modify a tag value of sub-table
-**Modify a tag name**
-```mysql
```mysql
ALTER TABLE tb_name SET TAG tag_name=new_tag_value;
ALTER STABLE stb_name CHANGE TAG old_tag_name new_tag_name;
```
```
Modify a tag name of STable. After modifying, all sub-tables under the STable will automatically update the new tag name.
Note: Except that the operation of tag value updating is carried out for sub-tables, all other tag operations (adding tags, deleting tags, etc.) can only be applied to STable, and cannot be operated on a single sub-table. After adding a tag to a STable, all tables established based on that will automatically add a new tag, and the default value is NULL.
-**Modify a tag value of sub-table**
```mysql
ALTER TABLE tb_name SET TAG tag_name=new_tag_value;
```
Note: Except that the operation of tag value updating is carried out for sub-tables, all other tag operations (adding tags, deleting tags, etc.) can only be applied to STable, and cannot be operated on a single sub-table. After adding a tag to a STable, all tables established based on that will automatically add a new tag, and the default value is NULL.
## <a class="anchor" id="insert"></a> Data Writing
## <a class="anchor" id="insert"></a> Data Writing
-Insert a record
-**Insert a record**
```mysql
```mysql
INSERT INTO tb_name VALUES (field_value, ...);
INSERT INTO tb_name VALUES (field_value, ...);
```
```
Insert a record into table tb_name.
Insert a record into table tb_name
-**Insert a record with data corresponding to a given column**
- Insert a record with data corresponding to a given column
```mysql
INSERT INTO tb_name (field1_name, ...) VALUES (field1_value1, ...);
Insert a record into table tb_name, and the data corresponds to a given column. For columns that do not appear in the SQL statement, database will automatically populate them with NULL. Primary key (timestamp) cannot be NULL.
```
Insert a record into table tb_name, and the data corresponds to a given column. For columns that do not appear in the SQL statement, database will automatically populate them with NULL. Primary key (timestamp) cannot be NULL.
- Insert multiple records
-```mysql
INSERT INTO tb_name VALUES (field1_value1, ...) (field1_value2, ...) ...;
Insert multiple records into tables tb1_name and tb2_name at the same time.
Insert multiple records per column into tables tb1_name and tb2_name at the same time
-**Insert multiple records per column into multiple tables**
Note: The timestamp of the oldest record allowed to be inserted is relative to the current server time, minus the configured keep value (days of data retention), and the timestamp of the latest record allowed to be inserted is relative to the current server time, plus the configured days value (interval of data storage in the data file, in days). Both keep and days can be specified when the database is created, and the default values are 3650 days and 10 days, respectively.
Insert multiple records per column into tables tb1_name and tb2_name at the same time.
Note: The timestamp of the oldest record allowed to be inserted is relative to the current server time, minus the configured keep value (days of data retention), and the timestamp of the latest record allowed to be inserted is relative to the current server time, plus the configured days value (interval of data storage in the data file, in days). Both keep and days can be specified when the database is created, and the default values are 3650 days and 10 days, respectively.
-<aclass="anchor"id="auto_create_table"></a> Automatically create a table when inserting
-<aclass="anchor"id="auto_create_table"></a> Automatically create a table when inserting
-```mysql
```mysql
INSERT INTO tb_name USING stb_name TAGS (tag_value1, ...) VALUES (field_value1, ...);
INSERT INTO tb_name USING stb_name TAGS (tag_value1, ...) VALUES (field_value1, ...);
```
```
If user is not sure whether a table exists when writing data, the automatic table building syntax can be used to create a non-existent table when writing. If the table already exists, no new table will be created. When automatically creating a table, it is required to use the STable as a template and specify tags value for the data table.
If user is not sure whether a table exists when writing data, the automatic table building syntax can be used to create a non-existent table when writing. If the table already exists, no new table will be created. When automatically creating a table, it is required to use the STable as a template and specify tags value for the data table.
- Automatically create a table when inserting, and specify a given tags column
During automatic table creation, only the values of some tags columns can be specified, and the unspecified tags columns will be null.
-**Automatically create a table when inserting, and specify a given tags column**
```mysql
INSERT INTO tb_name USING stb_name (tag_name1, ...) TAGS (tag_value1, ...) VALUES (field_value1, ...);
```
During automatic table creation, only the values of some tags columns can be specified, and the unspecified tags columns will be null.
**History writing**: The IMPORT or INSERT command can be used. The syntax and function of IMPORT are exactly the same as those of INSERT.
**History writing**: The IMPORT or INSERT command can be used. The syntax and function of IMPORT are exactly the same as those of INSERT.
- Look up table tb1 from 2018-06-01 08:00:00. 000 to 2018-06-02 08:00:00. 000, and col3 string is a record ending in'nny ', and the result is in descending order of timestamp:
- Look up table tb1 from 2018-06-01 08:00:00. 000 to 2018-06-02 08:00:00. 000, and col3 string is a record ending in'nny ', and the result is in descending order of timestamp:
-```mysql
```mysql
SELECT * FROM tb1 WHERE ts > '2018-06-01 08:00:00.000' AND ts <= '2018-06-02 08:00:00.000' AND col3 LIKE '%nny' ORDER BY ts DESC;
SELECT * FROM tb1 WHERE ts > '2018-06-01 08:00:00.000' AND ts <= '2018-06-02 08:00:00.000' AND col3 LIKE '%nny' ORDER BY ts DESC;
```
```
- Query the sum of col1 and col2, and name it complex. The time is greater than 2018-06-01 08:00:00. 000, and col2 is greater than 1.2. As a result, only 10 records are outputted, starting from item 5
- Query the sum of col1 and col2, and name it complex. The time is greater than 2018-06-01 08:00:00. 000, and col2 is greater than 1.2. As a result, only 10 records are outputted, starting from item 5
-```mysql
```mysql
SELECT (col1 + col2) AS 'complex' FROM tb1 WHERE ts > '2018-06-01 08:00:00.000' AND col2 > 1.2 LIMIT 10 OFFSET 5;
SELECT (col1 + col2) AS 'complex' FROM tb1 WHERE ts > '2018-06-01 08:00:00.000' AND col2 > 1.2 LIMIT 10 OFFSET 5;
```
```
- Query the records of past 10 minutes, the value of col2 is greater than 3.14, and output the result to the file /home/testoutpu.csv.
- Query the records of past 10 minutes, the value of col2 is greater than 3.14, and output the result to the file /home/testoutpu.csv.
-```mysql
```mysql
SELECT COUNT(*) FROM tb1 WHERE ts >= NOW - 10m AND col2 > 3.14 >> /home/testoutpu.csv;
SELECT COUNT(*) FROM tb1 WHERE ts >= NOW - 10m AND col2 > 3.14 >> /home/testoutpu.csv;
```
```
<aclass="anchor"id="functions"></a>
<aclass="anchor"id="functions"></a>
...
@@ -681,150 +695,172 @@ Query OK, 1 row(s) in set (0.001091s)
...
@@ -681,150 +695,172 @@ Query OK, 1 row(s) in set (0.001091s)
TDengine supports aggregations over data, they are listed below:
TDengine supports aggregations over data, they are listed below:
-**COUNT**
-**COUNT**
Function: record the number of rows or non-null values in a column of statistics/STable.
Returned result data type: long integer INT64.
Applicable Fields: Applied to all fields.
```mysql
SELECT COUNT([*|field_name]) FROM tb_name [WHERE clause];
Applied to: **table, STable**.
```
Function: record the number of rows or non-null values in a column of statistics/STable.
Note:
Returned result data type: long integer INT64.
1. 1. You can use \* instead of specific fields, and use *() to return the total number of records.
2. The query results for fields of the same table (excluding NULL values) are the same.
Applicable Fields: Applied to all fields.
3. If the statistic object is a specific column, return the number of records with non-NULL values in that column.
Applied to: **table, STable**.
Example:
Note:
-```mysql
1. You can use \* instead of specific fields, and use *() to return the total number of records.
taos> SELECT COUNT(*), COUNT(voltage) FROM meters;
2. The query results for fields of the same table (excluding NULL values) are the same.
count(*) | count(voltage) |
3. If the statistic object is a specific column, return the number of records with non-NULL values in that column.
================================================
9 | 9 |
Example:
Query OK, 1 row(s) in set (0.004475s)
```mysql
taos> SELECT COUNT(*), COUNT(voltage) FROM meters;
count(*) | count(voltage) |
================================================
9 | 9 |
Query OK, 1 row(s) in set (0.004475s)
taos> SELECT COUNT(*), COUNT(voltage) FROM d1001;
taos> SELECT COUNT(*), COUNT(voltage) FROM d1001;
count(*) | count(voltage) |
count(*) | count(voltage) |
================================================
================================================
3 | 3 |
3 | 3 |
Query OK, 1 row(s) in set (0.001075s)
Query OK, 1 row(s) in set (0.001075s)
```
```
- **AVG**
- **AVG**
-```mysql
```mysql
SELECT AVG(field_name) FROM tb_name [WHERE clause];
SELECT AVG(field_name) FROM tb_name [WHERE clause];
```
```
Function: return the average value of a column in statistics/STable.
Function: return the average value of a column in statistics/STable.
Return Data Type: double.
Applicable Fields: all types except timestamp, binary, nchar, bool.
Applied to: **table,STable**.
Example:
-```mysql
taos> SELECT AVG(current), AVG(voltage), AVG(phase) FROM meters;
SELECT STDDEV(field_name) FROM tb_name [WHERE clause];
SELECT STDDEV(field_name) FROM tb_name [WHERE clause];
```
Function: Mean square deviation of a column in statistics table.
Return Data Type: Double.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Applied to: **table**. (also support **STable** since version 2.0.15.1)
Example:
```mysql
taos> SELECT STDDEV(current) FROM d1001;
stddev(current) |
============================
1.020892909 |
Query OK, 1 row(s) in set (0.000915s)
```
```
Function: Mean square deviation of a column in statistics table.
Return Data Type: Double.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Applied to: **table**. (also support **STable** since version 2.0.15.1)
Example:
- **LEASTSQUARES**
- **LEASTSQUARES**
```mysql
Function: Value of a column in statistical table is a fitting straight equation of primary key (timestamp). Start_val is the initial value of independent variable, and step_val is the step size value of independent variable.
SELECT LEASTSQUARES(field_name, start_val, step_val) FROM tb_name [WHERE clause];
```
Return Data Type: String expression (slope, intercept).
Function: Value of a column in statistical table is a fitting straight equation of primary key (timestamp). Start_val is the initial value of independent variable, and step_val is the step size value of independent variable.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Return Data Type: String expression (slope, intercept).
Note: Independent variable is the timestamp, and dependent variable is the value of the column.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Applied to: **table**.
Note: Independent variable is the timestamp, and dependent variable is the value of the column.
Example:
Applied to: **table**.
Example:
```mysql
taos> SELECT LEASTSQUARES(current, 1, 1) FROM d1001;
SELECT LAST(field_name) FROM { tb_name | stb_name } [WHERE clause];
SELECT LAST(field_name) FROM { tb_name | stb_name } [WHERE clause];
```
```
Function: The last non-NULL value written by the value of a column in statistics/STable.
Function: The last non-NULL value written by the value of a column in statistics/STable.
Return Data Type: Same as applicable fields.
Return Data Type: Same as applicable fields.
Applicable Fields: All types.
Applicable Fields: All types.
Note:
Note:
1. To return the last (maximum timestamp) non-NULL value of each column, use LAST (\*);
1. 1. To return the last (maximum timestamp) non-NULL value of each column, use LAST (\*);
2. If a column in the result set has a NULL value, the returned result of the column is also NULL; if all columns in the result set have NULL values, no result is returned.
2. If a column in the result set has a NULL value, the returned result of the column is also NULL; if all columns in the result set have NULL values, no result is returned.
Function: The top k non-NULL values of a column in statistics/STable. If there are more than k column values tied for the largest, the one with smaller timestamp is returned.
Return Data Type: Same as applicable fields.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Note:
1. The range of *k* value is 1≤*k*≤100;
2. System also returns the timestamp column associated with the record.
Example:
Function: The top k non-NULL values of a column in statistics/STable. If there are more than k column values tied for the largest, the one with smaller timestamp is returned.
```mysql
taos> SELECT TOP(current, 3) FROM meters;
Return Data Type: Same as applicable fields.
ts | top(current, 3) |
=================================================
Applicable Fields: All types except timestamp, binary, nchar, bool.
2018-10-03 14:38:15.000 | 12.60000 |
2018-10-03 14:38:16.600 | 13.40000 |
Note:
2018-10-03 14:38:16.800 | 12.30000 |
Query OK, 3 row(s) in set (0.001548s)
1.*The range of k value is* 1≤*k*≤100;
2. System also returns the timestamp column associated with the record.
Example:
-```mysql
taos> SELECT TOP(current, 3) FROM meters;
ts | top(current, 3) |
=================================================
2018-10-03 14:38:15.000 | 12.60000 |
2018-10-03 14:38:16.600 | 13.40000 |
2018-10-03 14:38:16.800 | 12.30000 |
Query OK, 3 row(s) in set (0.001548s)
taos> SELECT TOP(current, 2) FROM d1001;
taos> SELECT TOP(current, 2) FROM d1001;
ts | top(current, 2) |
ts | top(current, 2) |
=================================================
=================================================
2018-10-03 14:38:15.000 | 12.60000 |
2018-10-03 14:38:15.000 | 12.60000 |
2018-10-03 14:38:16.800 | 12.30000 |
2018-10-03 14:38:16.800 | 12.30000 |
Query OK, 2 row(s) in set (0.000810s)
Query OK, 2 row(s) in set (0.000810s)
```
```
- **BOTTOM**
- **BOTTOM**
Function: The last k non-NULL values of a column in statistics/STable. If there are more than k column values tied for the smallest, the one with smaller timestamp is returned.
Function: The last k non-NULL values of a column in statistics/STable. If there are more than k column values tied for the smallest, the one with smaller timestamp is returned.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Return Data Type: Same as applicable fields.
Note:
Applicable Fields: All types except timestamp, binary, nchar, bool.
1.*The range of k value is* 1≤*k*≤100;
Note:
2. System also returns the timestamp column associated with the record.
1. The range of *k* value is 1≤*k*≤100;
2. System also returns the timestamp column associated with the record.
Example:
Example:
-```mysql
```mysql
taos> SELECT BOTTOM(voltage, 2) FROM meters;
taos> SELECT BOTTOM(voltage, 2) FROM meters;
ts | bottom(voltage, 2) |
ts | bottom(voltage, 2) |
===============================================
===============================================
2018-10-03 14:38:15.000 | 218 |
2018-10-03 14:38:15.000 | 218 |
2018-10-03 14:38:16.650 | 218 |
2018-10-03 14:38:16.650 | 218 |
Query OK, 2 row(s) in set (0.001332s)
Query OK, 2 row(s) in set (0.001332s)
taos> SELECT BOTTOM(current, 2) FROM d1001;
taos> SELECT BOTTOM(current, 2) FROM d1001;
ts | bottom(current, 2) |
ts | bottom(current, 2) |
=================================================
=================================================
2018-10-03 14:38:05.000 | 10.30000 |
2018-10-03 14:38:05.000 | 10.30000 |
2018-10-03 14:38:16.800 | 12.30000 |
2018-10-03 14:38:16.800 | 12.30000 |
Query OK, 2 row(s) in set (0.000793s)
Query OK, 2 row(s) in set (0.000793s)
```
```
- **PERCENTILE**
- **PERCENTILE**
```mysql
SELECT PERCENTILE(field_name, P) FROM { tb_name } [WHERE clause];
```
Function: Percentile of the value of a column in statistical table.
Return Data Type: Double.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Note: The range of P value is 0 ≤ P ≤ 100. P equals to MIN when, and equals MAX when it’s 100.
Example:
Function: Percentile of the value of a column in statistical table.
```mysql
Return Data Type: Double.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Note: The range of P value is 0 ≤ P ≤ 100. P equals to MIN when, and equals MAX when it’s 100.
Example:
```mysql
taos> SELECT PERCENTILE(current, 20) FROM d1001;
taos> SELECT PERCENTILE(current, 20) FROM d1001;
percentile(current, 20) |
percentile(current, 20) |
============================
============================
11.100000191 |
11.100000191 |
Query OK, 1 row(s) in set (0.000787s)
Query OK, 1 row(s) in set (0.000787s)
```
```
-
- **APERCENTILE**
- **APERCENTILE**
```mysql
Function: The value percentile of a column in statistical table is similar to the PERCENTILE function, but returns approximate results.
Function: The value percentile of a column in statistical table is similar to the PERCENTILE function, but returns approximate results.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Return Data Type: Double.
Note: The range of P value is 0 ≤ P ≤ 100. P equals to MIN when, and equals MAX when it’s 100. APERCENTILE function is recommended, which performs far better than PERCENTILE function.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Note: The range of *P* value is 0 ≤ *P* ≤ 100. *P* equals to MIN when, and equals MAX when it’s 100. APERCENTILE function is recommended, which performs far better than PERCENTILE function.
- **LAST_ROW**
- **LAST_ROW**
```mysql
SELECT LAST_ROW(field_name) FROM { tb_name | stb_name };
```
Function: Return the last record of a table (STtable).
Return Data Type: Double.
Applicable Fields: All types.
Note: Unlike last function, last_row does not support time range restriction and forces the last record to be returned.
Example:
Function: Return the last record of a table (STtable).
```mysql
taos> SELECT LAST_ROW(current) FROM meters;
Return Data Type: Double.
last_row(current) |
=======================
Applicable Fields: All types.
12.30000 |
Query OK, 1 row(s) in set (0.001238s)
Note: Unlike last function, last_row does not support time range restriction and forces the last record to be returned.
Example:
-```mysql
taos> SELECT LAST_ROW(current) FROM meters;
last_row(current) |
=======================
12.30000 |
Query OK, 1 row(s) in set (0.001238s)
taos> SELECT LAST_ROW(current) FROM d1002;
taos> SELECT LAST_ROW(current) FROM d1002;
last_row(current) |
last_row(current) |
=======================
=======================
10.30000 |
10.30000 |
Query OK, 1 row(s) in set (0.001042s)
Query OK, 1 row(s) in set (0.001042s)
```
```
### Computing Functions
### Computing Functions
- **DIFF**
- **DIFF**
Function: Return the value difference between a column and the previous column.
```mysql
SELECT DIFF(field_name) FROM tb_name [WHERE clause];
Return Data Type: Same as applicable fields.
```
Function: Return the value difference between a column and the previous column.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Return Data Type: Same as applicable fields.
Note: The number of output result lines is the total number of lines in the range minus one, and there is no result output in the first line.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Example:
Note: The number of output result lines is the total number of lines in the range minus one, and there is no result output in the first line.
Example:
-```mysql
```mysql
taos> SELECT DIFF(current) FROM d1001;
taos> SELECT DIFF(current) FROM d1001;
ts | diff(current) |
ts | diff(current) |
=================================================
=================================================
2018-10-03 14:38:15.000 | 2.30000 |
2018-10-03 14:38:15.000 | 2.30000 |
2018-10-03 14:38:16.800 | -0.30000 |
2018-10-03 14:38:16.800 | -0.30000 |
Query OK, 2 row(s) in set (0.001162s)
Query OK, 2 row(s) in set (0.001162s)
```
```
- **SPREAD**
- **SPREAD**
-```mysql
```mysql
SELECT SPREAD(field_name) FROM { tb_name | stb_name } [WHERE clause];
SELECT SPREAD(field_name) FROM { tb_name | stb_name } [WHERE clause];
```
```
Function: Return the difference between the max value and the min value of a column in statistics /STable.
Function: Return the difference between the max value and the min value of a column in statistics /STable.
Return Data Type: Same as applicable fields.
Return Data Type: Same as applicable fields.
Applicable Fields: All types except binary, nchar, bool.
Applicable Fields: All types except binary, nchar, bool.
Note: Applicable for TIMESTAMP field, which indicates the time range of a record.
Note: Applicable for TIMESTAMP field, which indicates the time range of a record.
Example:
Example:
-```mysql
```mysql
taos> SELECT SPREAD(voltage) FROM meters;
taos> SELECT SPREAD(voltage) FROM meters;
spread(voltage) |
spread(voltage) |
============================
============================
5.000000000 |
5.000000000 |
Query OK, 1 row(s) in set (0.001792s)
Query OK, 1 row(s) in set (0.001792s)
taos> SELECT SPREAD(voltage) FROM d1001;
taos> SELECT SPREAD(voltage) FROM d1001;
spread(voltage) |
spread(voltage) |
============================
============================
3.000000000 |
3.000000000 |
Query OK, 1 row(s) in set (0.000836s)
Query OK, 1 row(s) in set (0.000836s)
```
```
- Four Operations
Function: Calculation results of addition, subtraction, multiplication, division and remainder of values in a column or among multiple columns in statistics/STable.
Returned Data Type: Double.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Note:
- **Four Operations**
1. Calculation between two or more columns is supported, and the calculation priorities can be controlled by parentheses();
```mysql
2. The NULL field does not participate in the calculation. If a row involved in calculation contains NULL, the calculation result of the row is NULL.
Function: Calculation results of addition, subtraction, multiplication, division and remainder of values in a column or among multiple columns in statistics/STable.
Returned Data Type: Double.
Applicable Fields: All types except timestamp, binary, nchar, bool.
Note:
1. Calculation between two or more columns is supported, and the calculation priorities can be controlled by parentheses();
2. The NULL field does not participate in the calculation. If a row involved in calculation contains NULL, the calculation result of the row is NULL.
@@ -1151,18 +1194,18 @@ SELECT function_list FROM stb_name
...
@@ -1151,18 +1194,18 @@ SELECT function_list FROM stb_name
- WHERE statement specifies the start and end time of a query and other filters
- WHERE statement specifies the start and end time of a query and other filters
- FILL statement specifies a filling mode when data missed in a certain interval. Applicable filling modes include the following:
- FILL statement specifies a filling mode when data missed in a certain interval. Applicable filling modes include the following:
- - Do not fill: NONE (default filingl mode).
1. Do not fill: NONE (default filingl mode).
- VALUE filling: Fixed value filling, where the filled value needs to be specified. For example: fill (VALUE, 1.23).
2. VALUE filling: Fixed value filling, where the filled value needs to be specified. For example: fill (VALUE, 1.23).
- NULL filling: Fill the data with NULL. For example: fill (NULL).
3. NULL filling: Fill the data with NULL. For example: fill (NULL).
- PREV filling: Filling data with the previous non-NULL value. For example: fill (PREV).
4. PREV filling: Filling data with the previous non-NULL value. For example: fill (PREV).
- NEXT filling: Filling data with the next non-NULL value. For example: fill (NEXT).
5. NEXT filling: Filling data with the next non-NULL value. For example: fill (NEXT).
Note:
Note:
1. When using a FILL statement, a large number of filling outputs may be generated. Be sure to specify the time interval for the query. For each query, system can return no more than 10 million results with interpolation.
1. When using a FILL statement, a large number of filling outputs may be generated. Be sure to specify the time interval for the query. For each query, system can return no more than 10 million results with interpolation.
2. In a time-dimension aggregation, the time-series in returned results increases strictly monotonously.
2. In a time-dimension aggregation, the time-series in returned results increases strictly monotonously.
3. If the query object is a STable, the aggregator function will act on the data of all tables under the STable that meet the value filters. If group by statement is not used in the query, the returned result increases strictly monotonously according to time-series; If group by statement is used to group in the query, each group in the returned result does not increase strictly monotonously according to time-series.
3. If the query object is a STable, the aggregator function will act on the data of all tables under the STable that meet the value filters. If group by statement is not used in the query, the returned result increases strictly monotonously according to time-series; If group by statement is used to group in the query, each group in the returned result does not increase strictly monotonously according to time-series.
Example: The statement for building a database for smart meter is as follows:
Example: The statement for building a database for smart meter is as follows:
...
@@ -1200,4 +1243,4 @@ TAOS SQL supports join columns of two tables by Primary Key timestamp between th
...
@@ -1200,4 +1243,4 @@ TAOS SQL supports join columns of two tables by Primary Key timestamp between th
**Availability of is no null**
**Availability of is no null**
Is not null supports all types of columns. Non-null expression is <> "" and only applies to columns of non-numeric types.
Is not null supports all types of columns. Non-null expression is < > "" and only applies to columns of non-numeric types.
