Duplicate data in table I read some answered questions but they don't help me! This is my table: I want prevent duplicate data if their student_id and les_id were equal. How can I do it, I don't have much info about triggers......
* If requested, include information about GUC parameters with values that * don't match the built-in defaults. */ ExplainPrintSettings(es);}/* * ExplainPrintTriggers - * convert a QueryDesc's trigger statistics to text and append it to * es->str * * The caller should have set up t...
the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
Environment Suitability: It’s best to use this feature in development or testing environments rather than production, where the overhead and increased log volume might be less acceptable. auto_explain.log_triggers Purpose: This option logs details about triggers fired during quer...
The value of this parameter is in the format of maximum memory resource consumption/average memory resource consumption/minimum memory resource consumption. Example: mem=3528/1172/584B. An SQL statement may involve multiple operators. For more information about operators, see Operators. Note When...
and then finds a matchingrow in the second table, the third table, and so on. When all tables areprocessed, MySQL outputs the selected columns and backtracks through the tablelist until a table is found for which there are more matching rows. The nextrow is read from this table and the...
like trees because the master plan usually involves subplans. Any database worth its weight has such a thing though they may go by slightly different name - PostgreSQL, SQL Server, IBM DB2, Oracle, MySQL, Firebird, etc. PostgreSQL's flavor of it is fairly det...
PostgreSQL has tons of useful features and so it is somehow inevitable that some of it gets forgotten every now and then. In my case that's exactly what happens a lot with a cool piece of functionality called “auto_explain”, which is a module in the contrib package. So I thought I'...
SQL Server Explain Plan To get the execution plan from SQL Server, the query tool uses theSET SHOWPLAN_ALL ONcommand internally. After issuing this command, the tool executes the query in the query window, retrieves the plan, then issues SET SHOWPLAN_ALL OFF. Following this, the query in ...
SQL- Where Clause: Answer and Explanation: The purpose of ''Where'' clause in a query is to specify, to limit and to filter a condition when getting data from a table. Tables can be either be... Learn more about this topic: