<pre><codeclass="mysql language-mysql">SELECT TBNAME,[TAG_NAME,…] FROM <stable_name> WHERE <tag_name><[=|=<|>=|<>] values..> ([AND|OR] …)</code></pre>
<p>To delete a STable, all the tables created via this STable shall be deleted first, otherwise, it will fail.</p>
<p>To delete a STable, all the tables created via this STable will be deleted.</p>
<aclass='anchor'id='List-the-Associated-Tables-of-a-STable'></a><h3>List the Associated Tables of a STable</h3>
<pre><codeclass="mysql language-mysql">SELECT TBNAME,[TAG_NAME, ...] FROM <stable_name> WHERE <tag_name><[=|=<|>=|<>] values..> ([AND|OR] ...)</code></pre>
<p>It will list all the tables which satisfy the tag filter conditions. The tables are all created from this specific STable. TBNAME is a new keyword introduced, it is the table name associated with the STable. </p>
Note: For a table, the new record must have a timestamp bigger than the last data record, otherwise, it will be discarded and not inserted. If the timestamp is 0, the time stamp will be set to the system time on the server.
**IMPORT**: If you do want to insert a historical data record into a table, use IMPORT command instead of INSERT. IMPORT has the same syntax as INSERT. If you want to import a batch of historical records, the records must be ordered by the timestamp, otherwise, TDengine won't handle it in the right way.
Note: 1. For a table, the new record must have a timestamp bigger than the last data record, otherwise, it will be discarded and not inserted. If the timestamp is 0, the time stamp will be set to the system time on the server.
2.The timestamp of the oldest record allowed to be inserted is relative to the current server time, minus the configured keep value (the number of days the data is retained), and the timestamp of the latest record allowed to be inserted is relative to the current server time, plus the configured days value (the time span in which the data file stores data, in days). Both keep and days can be specified when creating the database. The default values are 3650 days and 10 days, respectively.
**IMPORT**: If you do want to insert a historical data record into a table, use IMPORT command instead of INSERT. IMPORT has the same syntax as INSERT.
@@ -62,7 +62,7 @@ Time series data is a sequence of data points over time. Inside a table, the dat
To reduce the development complexity and improve data consistency, TDengine provides the pub/sub functionality. To publish a message, you simply insert a record into a table. Compared with popular messaging tool Kafka, you subscribe to a table or a SQL query statement, instead of a topic. Once new data points arrive, TDengine will notify the application. The process is just like Kafka.
The detailed API will be introduced in the [connectors](https://www.taosdata.com/en/documentation/connector/) section.
The API documentation is at [C/C++ subscription API](https://www.taosdata.com/en/documentation/connector/#C/C++-subscription-API) section, and you can find more information from blog article (only Chinese version at present) [The usage of subscription](https://www.taosdata.com/blog/2020/02/12/1277.html).
##Caching
TDengine allocates a fixed-size buffer in memory, the newly arrived data will be written into the buffer first. Every device or table gets one or more memory blocks. For typical IoT scenarios, the hot data shall always be newly arrived data, they are more important for timely analysis. Based on this observation, TDengine manages the cache blocks in First-In-First-Out strategy. If no enough space in the buffer, the oldest data will be saved into hard disk first, then be overwritten by newly arrived data. TDengine also guarantees every device can keep at least one block of data in the buffer.
