mysql stored procedure "3"

First, let's explain the effect of the stored procedure function used:

Query each table name field in the data source table, query each table according to the table name, count the amount of data in each table, and then update the data source table.

The general situation of the data source table is as follows:

 Stored procedure:

DROP PROCEDURE
IF EXISTS updateDataSource;

CREATE PROCEDURE updateDataSource ()
BEGIN
	DECLARE
		dataSize INT DEFAULT 0;

DECLARE
	tableName VARCHAR (30);

DECLARE
	done INT DEFAULT FALSE;

DECLARE
	tableList CURSOR FOR SELECT
		data_table
	FROM
		data_source;

DECLARE
	CONTINUE HANDLER FOR NOT FOUND
SET done = TRUE;

OPEN tableList;

read_loop :
LOOP
	FETCH tableList INTO tableName;


IF done THEN
	LEAVE read_loop;


END
IF;


SET @STMT := CONCAT(
	"SELECT count(*) INTO @dataSize",
	" FROM ",
	tableName,
	";"
);

PREPARE STMT
FROM
	@STMT;

EXECUTE STMT;

DEALLOCATE PREPARE STMT;

UPDATE data_source
SET DATA_SIZE = @dataSize
WHERE
	DATA_TABLE = tableName;


END
LOOP
;

CLOSE tableList;


END

 Stored procedure description:

1. Take the value in the cursor in the LOOP loop and obtain each indication;

2. In order to dynamically use the table name in the stored procedure, define a sql statement @STMT, use function splicing, and assign the execution result of the sql statement to a variable for subsequent use;

3. PREPARE  STMT  FROM @ STMT , preprocessing sql, the scope is visible to the current client connection session; EXECUTE  STMT executes the preprocessed sql, if the executed STMT does not exist or is not defined, an error will be reported; DEALLOCATE PREPARE STMT releases the preprocessed sql sql resource;