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MySQL–DynamicSQLwithEXECUTEandPREPAREStatements_MySQL

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MySQL supports Dynamic SQL with the help of EXECUTE and PREPARE statements. Suppose you have a scenario where you need to pass table name as parameter value and returns all column values, you can use Dynamic SQL.

Let us create this table and data.

CREATE TABLE TestTable (ID INT, Col VARCHAR(4));
 INSERT INTO TestTable (ID, Col)
 SELECT 1, 'A'
 UNION ALL
 SELECT 1, 'B'
 UNION ALL
 SELECT 1, 'C'
 UNION ALL
 SELECT 2, 'A'
 UNION ALL
 SELECT 2, 'B'
 UNION ALL
 SELECT 2, 'C'
 UNION ALL
 SELECT 2, 'D'
 UNION ALL
 SELECT 2, 'E';

Now pass the table name as a parameter and returns all rows from it.

SET @table_name:='TestTable';
 SET @sql:=CONCAT('SELECT * FROM ',@table_name);
 PREPARE dynamic_statement FROM @sql;
 EXECUTE dynamic_statement;
 DEALLOCATE PREPARE dynamic_statement;

The variable @table_name is assigned name of the table. The variable @sql forms SELECT statement concatenating the Table name so the actual SELECT statement becomes SELECT * FROM TestTable. The PREPARE statement prepares the statement for execution and assigns a name (in this case it is dynamic_statement). EXECUTE command executes the statement prepared by the prepared name dynamic_statement and produces the result. The DEALLOCATE command releases the prepared statement.

So the result is

ID Col 1 A 1 B 1 C 2 A 2 B 2 C 2 D 2 E

Reference: Pinal Dave ( http://blog.sqlauthority.com )