A powerful tool to improve database processing speed - detailed explanation of MySQL stored procedures

Introduction to stored procedures

Our commonly used operating database language SQL statements need to be compiled first and then executed when executed, and the stored procedure (Stored Procedure) is a group of procedures designed to complete specific functions. A set of SQL statements is compiled and stored in the database. The user calls and executes the stored procedure by specifying the name and giving parameters (if the stored procedure has parameters).

A stored procedure is a programmable function that is created and saved in the database. It can consist of SQL statements and some special control structures. Stored procedures are useful when you want to perform the same function on different applications or platforms, or encapsulate specific functionality. Stored procedures in a database can be seen as a simulation of the object-oriented approach in programming. It allows control over how data is accessed.

Stored procedures usually have the following advantages:

1. Stored procedures enhance the functionality and flexibility of the SQL language. Stored procedures can be written using flow control statements, are highly flexible, and can complete complex judgments and more complex operations.

2. Stored procedures allow standard components to be programmed. After a stored procedure is created, it can be called multiple times in the program without having to rewrite the SQL statement of the stored procedure. And database professionals can modify stored procedures at any time without affecting the application source code.

3. Stored procedures can achieve faster execution speed. If an operation contains a large amount of Transaction-SQL code or is executed multiple times, the stored procedure will execute much faster than batch processing. Because stored procedures are precompiled. When a stored procedure is run for the first time, the query is analyzed and optimized by the optimizer and an execution plan is finally stored in the system table. The batch Transaction-SQL statement must be compiled and optimized every time it is run, and the speed is relatively slower.

4. Stored procedures can reduce network traffic. For operations on the same database object (such as query, modification), if the Transaction-SQL statement involved in this operation is organized into a stored procedure, then when the stored procedure is called on the client computer, only the call is transmitted over the network statements, thereby greatly increasing network traffic and reducing network load.

5. Stored procedures can be fully utilized as a security mechanism. By restricting the permissions for executing a certain stored procedure, the system administrator can limit the access permissions of the corresponding data, avoid unauthorized users from accessing the data, and ensure the security of the data.

Stored procedures are an important function of database storage, but MySQL did not support stored procedures before 5.0, which greatly reduced the application of MySQL. Fortunately, MySQL 5.0 has finally begun to support stored procedures, which can greatly improve the processing speed of the database and also improve the flexibility of database programming.

Create stored procedure

1. Format

MySQL stored procedure creation format:

mysql> DELIMITER // 
mysql> CREATE PROCEDURE proc1(OUT s int) 
     -> BEGIN 
     -> SELECT COUNT(*) INTO s FROM user; 
     -> END 
     -> // 
mysql> DELIMITER ;

Note:

1. What needs to be noted here is DELIMITER // and DELIMITER ; in two sentences, DELIMITER means delimiter, because MySQL uses ";" as the delimiter by default. If we do not declare a delimiter, then the compiler The stored procedure will be processed as a SQL statement, and the compilation process of the stored procedure will report an error, so you must use the DELIMITER keyword to declare the current segment separator in advance, so that MySQL will treat ";" as the code in the stored procedure and will not execute it. After using these codes, you need to restore the separators.

2. The stored procedure may have input, output, input and output parameters as needed. There is an output parameter s, the type is int. If there are multiple parameters, use "," to separate them. .

3. The beginning and end of the process body are marked with BEGIN and END.

In this way, one of our MySQL stored procedures is completed. Isn’t it easy? It doesn’t matter if you don’t understand it. Next, we will explain it in detail.

2. Declaration separator

In fact, regarding the declaration separator, the above annotation has been written very clearly. There is no need to say more, but you need to pay a little attention. Yes: If you are using the MySQL Administrator management tool, you can create it directly and no longer need to declare it.

3. Parameters

The parameters of MySQL stored procedures are used in the definition of stored procedures. There are three parameter types - IN, OUT, INOUT. The form is as follows ：

CREATE PROCEDURE([[IN |OUT |INOUT ] 参数名 数据类形...])

IN Input parameter: Indicates that the value of this parameter must be specified when calling the stored procedure. If the value of this parameter is modified during the stored procedure, it cannot be returned and is the default value.

OUT Output parameter : The value can be changed inside the stored procedure and can be returned

INOUT Input and output parameters: specified when calling, and can be changed and returned

1) IN parameter example

Creation:

mysql > DELIMITER // 
mysql > CREATE PROCEDURE demo_in_parameter(IN p_in int) 
    -> BEGIN 
    -> SELECT p_in; 
    -> SET p_in=2; 
    -> SELECT p_in; 
    -> END; 
    -> // 
mysql > DELIMITER ;

Execution result:

mysql > SET @p_in=1;
mysql > CALL demo_in_parameter(@p_in);
+------+
| p_in |
+------+
| 1 |
+------+

+------+
| p_in |
+------+
| 2 |
+------+

mysql> SELECT @p_in;
+-------+
| @p_in |
+-------+
| 1 |
+-------+

As can be seen from the above, although p_in is modified during the stored procedure, it does not affect the value of @p_id.

2) OUT parameter example

Creation:

mysql > DELIMITER // 
mysql > CREATE PROCEDURE demo_out_parameter(OUT p_out int) 
    -> BEGIN 
    -> SELECT p_out; 
    -> SET p_out=2; 
    -> SELECT p_out; 
    -> END; 
    -> // 
mysql > DELIMITER;

Execution result:

mysql > SET @p_out=1;
mysql > CALL sp_demo_out_parameter(@p_out);
+-------+
| p_out |
+-------+
| NULL |
+-------+

+-------+
| p_out |
+-------+
| 2 |
+-------+

mysql> SELECT @p_out;
+-------+
| p_out |
+-------+
| 2 |
+-------+

3) INOUT parameter example

Creation:

 mysql > DELIMITER //
 mysql > CREATE PROCEDURE demo_inout_parameter(INOUT p_inout int)
     -> BEGIN
     -> SELECT p_inout;
     -> SET p_inout=2;
     -> SELECT p_inout;
     -> END;
     -> //
 mysql > DELIMITER;

Execution result:

mysql > SET @p_inout=1;
mysql > CALL demo_inout_parameter(@p_inout) ;
+---------+
| p_inout |
+---------+
| 1 |
+---------+

+---------+
| p_inout |
+---------+
| 2 |
+---------+

mysql > SELECT @p_inout;
+----------+
| @p_inout |
+----------+
| 2 |
+----------+

4, variable

1）变量定义

DECLARE variable_name [,variable_name...] datatype [DEFAULT value];

其中，datatype为MySQL的数据类型，如：int、 float、 date、varchar(length)，例如:

DECLARE l_int int unsigned default 4000000; 
DECLARE l_numeric number(8,2) DEFAULT 9.95; 
DECLARE l_date date DEFAULT '1999-12-31'; 
DECLARE l_datetime datetime DEFAULT '1999-12-31 23:59:59'; 
DECLARE l_varchar varchar(255) DEFAULT 'This will not be padded';

2）变量赋值

SET 变量名 = 表达式值 [,variable_name = expression ...]

3）用户变量

在MySQL客户端使用用户变量：

mysql > SELECT 'Hello World' into @x;
mysql > SELECT @x;
+-------------+
| @x |
+-------------+
| Hello World |
+-------------+
mysql > SET @y='Goodbye Cruel World';
mysql > SELECT @y;
+---------------------+
| @y |
+---------------------+
| Goodbye Cruel World |
+---------------------+

mysql > SET @z=1+2+3;
mysql > SELECT @z;
+------+
| @z |
+------+
| 6 |
+------+

在存储过程中使用用户变量：

mysql > CREATE PROCEDURE GreetWorld( ) SELECT CONCAT(@greeting,' World');
mysql > SET @greeting='Hello';
mysql > CALL GreetWorld( );
+----------------------------+
| CONCAT(@greeting,' World') |
+----------------------------+
| Hello World |
+----------------------------+

在存储过程间传递全局范围的用户变量：

mysql> CREATE PROCEDURE p1() SET @last_procedure='p1';
mysql> CREATE PROCEDURE p2() SELECT CONCAT('Last procedure was ',@last_proc);
mysql> CALL p1( );
mysql> CALL p2( );
+-----------------------------------------------+
| CONCAT('Last procedure was ',@last_proc |
+-----------------------------------------------+
| Last procedure was p1 |
+-----------------------------------------------+

注意：用户变量名一般以@开头，滥用用户变量会导致程序难以理解及管理

5、注释

MySQL存储过程可使用两种风格的注释

• 双模杠：--（该风格一般用于单行注释）

• C语言风格： 一般用于多行注释

例如：

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc1 --name存储过程名 
    -> (IN parameter1 INTEGER) 
    -> BEGIN 
    -> DECLARE variable1 CHAR(10); 
    -> IF parameter1 = 17 THEN 
    -> SET variable1 = 'birds'; 
    -> ELSE 
    -> SET variable1 = 'beasts'; 
    -> END IF; 
    -> INSERT INTO table1 VALUES (variable1); 
    -> END 
    -> // 
mysql > DELIMITER ;

调用存储过程

用call和你过程名以及一个括号，括号里面根据需要，加入参数，参数包括输入参数、输出参数、输入输出参数。具体的调用方法可以参看上面的例子。

查询存储过程

我们像知道一个数据库下面有那些表，我们一般采用show tables;进行查看。那么我们要查看某个数据库下面的存储过程，是否也可以采用呢？答案是，我们可以查看某个数据库下面的存储过程，但是是令一钟方式。我们可以用

select name from mysql.proc where db=’数据库名’;

或者

select routine_name from information_schema.routines where routine_schema='数据库名';

或者

show procedure status where db='数据库名';

进行查询。

如果我们想知道，某个存储过程的详细，那我们又该怎么做呢？是不是也可以像操作表一样用describe 表名进行查看呢？

答案是：我们可以查看存储过程的详细，但是需要用另一种方法：

SHOW CREATE PROCEDURE 数据库.存储过程名;

就可以查看当前存储过程的详细。

修改存储过程

ALTER PROCEDURE

更改用CREATE PROCEDURE 建立的预先指定的存储过程，其不会影响相关存储过程或存储功能。

删除存储过程

删除一个存储过程比较简单，和删除表一样：

DROP PROCEDURE

从MySQL的表格中删除一个或多个存储过程。

存储过程的控制语句

1、变量作用域

内部的变量在其作用域范围内享有更高的优先权，当执行到end。变量时，内部变量消失，此时已经在其作用域外，变量不再可见了，应为在存储
过程外再也不能找到这个申明的变量，但是你可以通过out参数或者将其值指派给会话变量来保存其值。

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc3() 
    -> begin 
    -> declare x1 varchar(5) default 'outer'; 
    -> begin 
    -> declare x1 varchar(5) default 'inner'; 
    -> select x1; 
    -> end; 
    -> select x1; 
    -> end; 
    -> // 
mysql > DELIMITER ;

2、条件语句

if-then -else语句

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc2(IN parameter int) 
    -> begin 
    -> declare var int; 
    -> set var=parameter+1; 
    -> if var=0 then 
    -> insert into t values(17); 
    -> end if; 
    -> if parameter=0 then 
    -> update t set s1=s1+1; 
    -> else 
    -> update t set s1=s1+2; 
    -> end if; 
    -> end; 
    -> // 
mysql > DELIMITER ;

case语句：

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc3 (in parameter int) 
    -> begin 
    -> declare var int; 
    -> set var=parameter+1; 
    -> case var 
    -> when 0 then 
    -> insert into t values(17); 
    -> when 1 then 
    -> insert into t values(18); 
    -> else 
    -> insert into t values(19); 
    -> end case; 
    -> end; 
    -> // 
mysql > DELIMITER ;

3、循环语句

while ···· end while：

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc4() 
    -> begin 
    -> declare var int; 
    -> set var=0; 
    -> while var<6 do 
    -> insert into t values(var); 
    -> set var=var+1; 
    -> end while; 
    -> end; 
    -> // 
mysql > DELIMITER ;

repeat···· end repeat：

它在执行操作后检查结果，而while则是执行前进行检查。

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc5 () 
    -> begin 
    -> declare v int; 
    -> set v=0; 
    -> repeat 
    -> insert into t values(v); 
    -> set v=v+1; 
    -> until v>=5 
    -> end repeat; 
    -> end; 
    -> // 
mysql > DELIMITER ;

loop ·····end loop:

loop循环不需要初始条件，这点和while 循环相似，同时和repeat循环一样不需要结束条件, leave语句的意义是离开循环。

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc6 () 
    -> begin 
    -> declare v int; 
    -> set v=0; 
    -> LOOP_LABLE:loop 
    -> insert into t values(v); 
    -> set v=v+1; 
    -> if v >=5 then 
    -> leave LOOP_LABLE; 
    -> end if; 
    -> end loop; 
    -> end; 
    -> // 
mysql > DELIMITER ;

LABLES 标号：

标号可以用在begin repeat while 或者loop 语句前，语句标号只能在合法的语句前面使用。可以跳出循环，使运行指令达到复合语句的最后一步。

4、ITERATE迭代

ITERATE：通过引用复合语句的标号,来从新开始复合语句

mysql > DELIMITER // 
mysql > CREATE PROCEDURE proc10 () 
    -> begin 
    -> declare v int; 
    -> set v=0; 
    -> LOOP_LABLE:loop 
    -> if v=3 then 
    -> set v=v+1; 
    -> ITERATE LOOP_LABLE; 
    -> end if; 
    -> insert into t values(v); 
    -> set v=v+1; 
    -> if v>=5 then 
    -> leave LOOP_LABLE; 
    -> end if; 
    -> end loop; 
    -> end; 
    -> // 
mysql > DELIMITER ;

MySQL存储过程的基本函数

1、字符串类

CHARSET(str) //返回字串字符集
CONCAT (string2 [,... ]) //连接字串
INSTR (string ,substring ) //返回substring首次在string中出现的位置,不存在返回0
LCASE (string2 ) //转换成小写
LEFT (string2 ,length ) //从string2中的左边起取length个字符
LENGTH (string ) //string长度
LOAD_FILE (file_name ) //从文件读取内容
LOCATE (substring , string [,start_position ] ) 同INSTR,但可指定开始位置
LPAD (string2 ,length ,pad ) //重复用pad加在string开头,直到字串长度为length
LTRIM (string2 ) //去除前端空格
REPEAT (string2 ,count ) //重复count次
REPLACE (str ,search_str ,replace_str ) //在str中用replace_str替换search_str
RPAD (string2 ,length ,pad) //在str后用pad补充,直到长度为length
RTRIM (string2 ) //去除后端空格
STRCMP (string1 ,string2 ) //逐字符比较两字串大小
SUBSTRING (str , position [,length ]) //从str的position开始,取length个字符

注：mysql中处理字符串时，默认第一个字符下标为1，即参数position必须大于等于1

mysql> select substring('abcd',0,2);
+-----------------------+
| substring('abcd',0,2) |
+-----------------------+
| |
+-----------------------+
1 row in set (0.00 sec)

mysql> select substring('abcd',1,2);
+-----------------------+
| substring('abcd',1,2) |
+-----------------------+
| ab |
+-----------------------+
1 row in set (0.02 sec)
TRIM([[BOTH|LEADING|TRAILING] [padding] FROM]string2) //去除指定位置的指定字符
UCASE (string2 ) //转换成大写
RIGHT(string2,length) //取string2最后length个字符
SPACE(count) //生成count个空格

2、数学类

ABS (number2 ) //绝对值
BIN (decimal_number ) //十进制转二进制
CEILING (number2 ) //向上取整
CONV(number2,from_base,to_base) //进制转换
FLOOR (number2 ) //向下取整
FORMAT (number,decimal_places ) //保留小数位数
HEX (DecimalNumber ) //转十六进制
注：HEX()中可传入字符串，则返回其ASC-11码，如HEX('DEF')返回4142143
也可以传入十进制整数，返回其十六进制编码，如HEX(25)返回19
LEAST (number , number2 [,..]) //求最小值
MOD (numerator ,denominator ) //求余
POWER (number ,power ) //求指数
RAND([seed]) //随机数
ROUND (number [,decimals ]) //四舍五入,decimals为小数位数]

注：返回类型并非均为整数，如：

默认变为整形值

mysql> select round(1.23);
+-------------+
| round(1.23) |
+-------------+
| 1 |
+-------------+
1 row in set (0.00 sec)

mysql> select round(1.56);
+-------------+
| round(1.56) |
+-------------+
| 2 |
+-------------+
1 row in set (0.00 sec)

可以设定小数位数，返回浮点型数据

mysql> select round(1.567,2); 
+----------------+ 
| round(1.567,2) | 
+----------------+ 
| 1.57 | 
+----------------+ 
1 row in set (0.00 sec) 
SIGN (number2 ) //

3、日期时间类

ADDTIME (date2 ,time_interval ) //将time_interval加到date2
CONVERT_TZ (datetime2 ,fromTZ ,toTZ ) //转换时区
CURRENT_DATE ( ) //当前日期
CURRENT_TIME ( ) //当前时间
CURRENT_TIMESTAMP ( ) //当前时间戳
DATE (datetime ) //返回datetime的日期部分
DATE_ADD (date2 , INTERVAL d_value d_type ) //在date2中加上日期或时间
DATE_FORMAT (datetime ,FormatCodes ) //使用formatcodes格式显示datetime
DATE_SUB (date2 , INTERVAL d_value d_type ) //在date2上减去一个时间
DATEDIFF (date1 ,date2 ) //两个日期差
DAY (date ) //返回日期的天
DAYNAME (date ) //英文星期
DAYOFWEEK (date ) //星期(1-7) ,1为星期天
DAYOFYEAR (date ) //一年中的第几天
EXTRACT (interval_name FROM date ) //从date中提取日期的指定部分
MAKEDATE (year ,day ) //给出年及年中的第几天,生成日期串
MAKETIME (hour ,minute ,second ) //生成时间串
MONTHNAME (date ) //英文月份名
NOW ( ) //当前时间
SEC_TO_TIME (seconds ) //秒数转成时间
STR_TO_DATE (string ,format ) //字串转成时间,以format格式显示
TIMEDIFF (datetime1 ,datetime2 ) //两个时间差
TIME_TO_SEC (time ) //时间转秒数]
WEEK (date_time [,start_of_week ]) //第几周
YEAR (datetime ) //年份
DAYOFMONTH(datetime) //月的第几天
HOUR(datetime) //小时
LAST_DAY(date) //date的月的最后日期
MICROSECOND(datetime) //微秒
MONTH(datetime) //月
MINUTE(datetime) //分返回符号,正负或0
SQRT(number2) //开平方

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