存储过程中使用 SQL 语句(转)

1，使用非SELECT语句

UPDATE/INSERT/SET、DDL、DML等非查询语句可以随意在存储程序里执行

CREATE PROCEDURE simple_sqls()

BEGIN

DECLARE i INT DEFAULT 1;

/* Example of a utility statement */

DROP TABLE IF EXISTS test_table

CREATE TABLE test_table

(id INT PRIMARY KEY, some_data VARCHAR(30)) ENGINE=innodb;

/* Example of an INSERT using a procedure variable */

WHILE (i<=10) DO

INSERT INTO TEST_TABLE VALUES(i, CONCAT("record ", i));

SET i=i+1;

END WHILE

/* Example of an UPDATE using procedure variabless */

SET i =5;

UPDATE test_table

SET some_data=CONCAT("I updated row ", i)

WHERE id=i;

/* DELETE with a procedure variable */

DELETE FROM test_table

WHERE id>i;

END;

CREATE PROCEDURE simple_sqls()
BEGIN
DECLARE i INT DEFAULT 1;
/* Example of a utility statement */
DROP TABLE IF EXISTS test_table
CREATE TABLE test_table
(id INT PRIMARY KEY, some_data VARCHAR(30)) ENGINE=innodb;
/* Example of an INSERT using a procedure variable */
WHILE (i<=10) DO
INSERT INTO TEST_TABLE VALUES(i, CONCAT("record ", i));
SET i=i+1;
END WHILE
/* Example of an UPDATE using procedure variabless */
SET i =5;
UPDATE test_table
SET some_data=CONCAT("I updated row ", i)
WHERE id=i;
/* DELETE with a procedure variable */
DELETE FROM test_table
WHERE id>i;
END;

2，使用INTO

如果SELECT语句只返回一行记录，则可以使用INTO语句来把结果存入一个变量

如果SELECT语句返回多行记录，则使用INTO会出现运行时错误

CREATE PROCEDURE get_customer_details(in_customer_id INT)

BEGIN

DECLARE l_customer_name VARCHAR(30);

DECLARE l_contact_surname VARCHAR(30);

DECLARE l_contact_firstname VARCHAR(30);

SELECT customer_name, contact_surname, contact_firstname

INTO l_customer_name, l_contact_surname, contact_firstname

FROM customers

WHERE customer_id=in_customer_id;

/* Do something with the customer record */

END;

CREATE PROCEDURE get_customer_details(in_customer_id INT)
BEGIN
DECLARE l_customer_name     VARCHAR(30);
DECLARE l_contact_surname   VARCHAR(30);
DECLARE l_contact_firstname VARCHAR(30);
SELECT customer_name, contact_surname, contact_firstname
INTO l_customer_name, l_contact_surname, contact_firstname
FROM customers
WHERE customer_id=in_customer_id;
/* Do something with the customer record */
END;

3，创建和使用Cursor

可以使用Cursor来处理SELECT语句返回多好记录时的场景

Cursor提供对查询结果集的访问，并且可以循环结果集的每一行，然后每行单独处理

DECLARE l_dept_id BIGINT;

DECLARE c_dept CURSOR FOR

SELECT department_id FROM departments;

OPEN c_dept;

dept_cursor: LOOP

FETCH c_dept INTO l_dept_id;

END LOOP dept_cursor;

CLOSE c_dept;

DECLARE l_dept_id BIGINT;
DECLARE c_dept CURSOR FOR
SELECT department_id FROM departments;
OPEN c_dept;
dept_cursor: LOOP
FETCH c_dept INTO l_dept_id;
END LOOP dept_cursor;
CLOSE c_dept;

存在的第一个问题：变量声明必须在CURSOR声明之前

存在的第二个问题：上面的程序在FETCH结果集遇到最后一条之后会报错"no data to fetch" error (MySQL error 1329; SQLSTATE 02000)

为了避免第二个问题，我们需要声明一个HANDLER

DECLARE l_dept_id BIGINT;

DECLARE l_last_row_fetched INT;

DECLARE c_dept CURSOR FOR

SELECT department_id FROM departments;

DECLARE CONTINUE HANDLER FOR NOT FOUND SET l_last_row_fetched=1;

SET l_last_row_fetched=0;

OPEN c_dept;

dept_cursor: LOOP

FETCH c_dept INTO l_dept_id;

IF l_last_row_fetched=1 THEN

LEAVE dept_cursor;

END IF;

END LOOP dept_cursor;

CLOSE c_dept;

SET l_last_row_fetched=0;

DECLARE l_dept_id BIGINT;
DECLARE l_last_row_fetched INT;
DECLARE c_dept CURSOR FOR
SELECT department_id FROM departments;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET l_last_row_fetched=1;
SET l_last_row_fetched=0;
OPEN c_dept;
dept_cursor: LOOP
FETCH c_dept INTO l_dept_id;
IF l_last_row_fetched=1 THEN
LEAVE dept_cursor;
END IF;
END LOOP dept_cursor;
CLOSE c_dept;
SET l_last_row_fetched=0;

4，使用UNBOUNED SELECT语句返回数据给调用者

sp:

CREATE PROCEDCURE sp_get_all_users()

BEGIN

SELECT user_name, age

FROM users;

END;

CREATE PROCEDCURE sp_get_all_users()
BEGIN
SELECT user_name, age
FROM users;
END;

客户端:

private void getAllUsers(Connection c) throws SQLException {

CallableStatement s = c.prepareCall("{CALL sp_get_all_users()}");

s.execute();

ResultSet rs = s.getResultSet();

while(rs.next()) {

System.out.println(rs.getString("user_name"));

}

rs.close();

s.close();

}

private void getAllUsers(Connection c) throws SQLException {
CallableStatement s = c.prepareCall("{CALL sp_get_all_users()}");
s.execute();
ResultSet rs = s.getResultSet();
while(rs.next()) {
System.out.println(rs.getString("user_name"));
}
rs.close();
s.close();
}

5，使用Prepared Statements处理动态SQL

MySQL支持server-side prepared statements，PREPARE创建，EXECUTE执行，DEALLOCATE销毁:

mysql> PREPARE prod_insert_stmt FROM "INSERT INTO product_codes VALUES(?,?)";

Query OK, 0 rows affected (0.00 sec)

Statement prepared

mysql>

mysql> SET @code='QB';

Query OK, 0 rows affected (0.00 sec)

mysql> SET @name='MySQL Query Browser';

Query OK, 0 rows affected (0.00 sec)

mysql> EXECUTE prod_insert_stmt USING @code,@name;

Query OK, 1 row affected (0.00 sec)

mysql> SET @code='AD';

Query OK, 0 rows affected (0.00 sec)

mysql> SET @name='MySQL Administrator';

Query OK, 0 rows affected (0.02 sec)

mysql> EXECUTE prod_insert_stmt USING @code,@name;

Query OK, 1 row affected (0.00 sec)

mysql> DEALLOCATE PREPARE prod_insert_stmt;

Query OK, 0 rows affected (0.00 sec)

mysql> PREPARE prod_insert_stmt FROM "INSERT INTO product_codes VALUES(?,?)";
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql>
mysql> SET @code='QB';
Query OK, 0 rows affected (0.00 sec)
mysql> SET @name='MySQL Query Browser';
Query OK, 0 rows affected (0.00 sec)
mysql> EXECUTE prod_insert_stmt USING @code,@name;
Query OK, 1 row affected (0.00 sec)
mysql> SET @code='AD';
Query OK, 0 rows affected (0.00 sec)
mysql> SET @name='MySQL Administrator';
Query OK, 0 rows affected (0.02 sec)
mysql> EXECUTE prod_insert_stmt USING @code,@name;
Query OK, 1 row affected (0.00 sec)
mysql> DEALLOCATE PREPARE prod_insert_stmt;
Query OK, 0 rows affected (0.00 sec)

这样一来就可以在sp里做一些手脚，让sp更flexible:

CREATE PROCEDURE set_col_value

(in_table VARCHAR(128),

in_column VARCHAR(128),

in_new_value VARCHAR(1000),

in_where VARCHAR(4000))

BEGIN

DECLARE l_sql VARCHAR(4000);

SET l_slq=CONCAT_ws(' ',

'UPDATE', in_table,

'SET', in_column, '=', in_new_value,

'WHERE', in_where);

SET @sql=l_sql;

PREPARE s1 FROM @sql;

EXECUTE s1;

DEALLOCATE PREPARE s1;

END;

CREATE PROCEDURE set_col_value
(in_table     VARCHAR(128),
in_column    VARCHAR(128),
in_new_value VARCHAR(1000),
in_where     VARCHAR(4000))
BEGIN
DECLARE l_sql VARCHAR(4000);
SET l_slq=CONCAT_ws(' ',
'UPDATE', in_table,
'SET', in_column, '=', in_new_value,
'WHERE', in_where);
SET @sql=l_sql;
PREPARE s1 FROM @sql;
EXECUTE s1;
DEALLOCATE PREPARE s1;
END;

6，声明HANDLER的语法

DECLARE {CONTINUE | EXIT} HANDLER FOR

{SQLSTATE sqlstate_code | MySQL error code | condition_name}

stored_program_statement

DECLARE {CONTINUE | EXIT} HANDLER FOR
{SQLSTATE sqlstate_code | MySQL error code | condition_name}
stored_program_statement