[英]Run a query in a MySQL stored procedure if a condition is true
我正在使用MySQL數據庫並嘗試創建存儲過程。 我如何才能做到,如果query1的結果沒有記錄,那么它將執行另一個查詢?
這是我到目前為止的內容:
/* CREATE DB */
CREATE DATABASE mydata;
use mydata;
/* TABLE */
CREATE TABLE mydata (
ID BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
Name VARCHAR(255) NOT NULL,
Value VARCHAR(255) NOT NULL
) ENGINE=InnoDB;
INSERT INTO mydata (Name, Value) VALUES ("testname", "testvalue");
/* STORED PROCEDURE */
delimiter //
CREATE PROCEDURE myproc(IN myTable VARCHAR(255),
IN myValue VARCHAR(255),
IN myValueTwo VARCHAR(255))
BEGIN
SET @iTable=myTable;
SET @iValue=myValue;
SET @iValueTwo=myValueTwo;
SET @query = CONCAT('SELECT Name FROM ', @iTable,
' WHERE Value="', @iValue, '"');
SET @querytwo = CONCAT('SELECT Name FROM ', @iTable,
' WHERE Value="', @iValueTwo, '"');
PREPARE QUERY FROM @query;
EXECUTE QUERY;
END //
delimiter ;
/* CALL */
call myproc("mydata", "testvalue", "");
我想運行一個查詢,並且僅在第一個沒有行的情況下才執行第二個查詢。 做這個的最好方式是什么?
這花了一些工夫,但我做了足夠的調整。 您的代碼問題與您的邏輯無關,但與MySQL存儲過程語言本身無關。 在執行動態SQL時,存在范圍問題。
我所做的是創建一個臨時表並將返回的值存放在其中
這是一些示例數據
mysql> drop database if exists user391986;
Query OK, 1 row affected (0.08 sec)
mysql> create database user391986;
Query OK, 1 row affected (0.00 sec)
mysql> use user391986
Database changed
mysql> CREATE TABLE mytable (
-> ID BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
-> Name VARCHAR(255) NOT NULL,
-> Value VARCHAR(255) NOT NULL
-> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.11 sec)
mysql> INSERT INTO mytable (Name,Value) VALUES
-> ('rolando','edge'),('pamela','washington'),
-> ('dominique','wilkins'),('diamond','cutter');
Query OK, 4 rows affected (0.06 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> SELECT * from mytable;
+----+-----------+------------+
| ID | Name | Value |
+----+-----------+------------+
| 1 | rolando | edge |
| 2 | pamela | washington |
| 3 | dominique | wilkins |
| 4 | diamond | cutter |
+----+-----------+------------+
4 rows in set (0.00 sec)
mysql>
這是為適應臨時表中的返回值而進行調整的存儲過程
mysql> delimiter //
mysql> CREATE PROCEDURE myproc(IN myTable VARCHAR(255), IN myValue VARCHAR(255), IN myValueTwo VARCHAR(255))
-> BEGIN
-> DECLARE foundcount INT;
-> DECLARE retval VARCHAR(255);
->
-> SET @iTable=myTable;
-> SET @iValue=myValue;
-> SET @iValueTwo=myValueTwo;
->
-> CREATE TEMPORARY TABLE IF NOT EXISTS mynumber (rv VARCHAR(255)) ENGINE=MEMORY;
-> DELETE FROM mynumber;
->
-> SET retval = 'nothing retrieved';
-> SET @query = CONCAT('INSERT INTO mynumber SELECT Name FROM ', @iTable, ' WHERE Value=''', @iValue, '''');
-> PREPARE QUERY FROM @query;
-> EXECUTE QUERY;
-> DEALLOCATE PREPARE QUERY;
-> SELECT COUNT(1) INTO foundcount FROM mynumber;
-> IF foundcount = 0 THEN
-> SET @querytwo = CONCAT('INSERT INTO mynumber SELECT Name FROM ', @iTable, ' WHERE Value=''', @iValueTwo, '''');
-> PREPARE QUERY FROM @querytwo;
-> EXECUTE QUERY;
-> DEALLOCATE PREPARE QUERY;
-> END IF;
-> SELECT COUNT(1) INTO foundcount FROM mynumber;
-> IF foundcount > 0 THEN
-> SELECT rv INTO retval FROM mynumber;
-> END IF;
-> SELECT retval;
->
-> END //
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
mysql>
好的,我三次調用了存儲過程。 首先什么也沒有。 第二個獲得第二個值。 第三個獲得第一個值。
mysql> CALL myproc('mytable','pamela','diamond');
+-------------------+
| retval |
+-------------------+
| nothing retrieved |
+-------------------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.02 sec)
mysql> CALL myproc('mytable','pamela','wilkins');
+-----------+
| retval |
+-----------+
| dominique |
+-----------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.01 sec)
mysql> CALL myproc('mytable','edge','wilkins');
+---------+
| retval |
+---------+
| rolando |
+---------+
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.02 sec)
mysql>
試試看 !!!
在Sql Server中,您可以將結果運行到臨時表中,然后檢查temp表中是否存在如下行:
declare @numberResults int = 0
create table #MyTempTable(...)
insert #MyTempTable
sp_executesql Query
set @numberResults = (select count(*) from #MyTempTable)
if @numberResults = 0
begin
sp_executesql secondQuery
end
在mysql中,您可以使用內置的found_rows()
過程,如下所示:
el@apollo:~$ mysql -u root -p
Enter password:
mysql> use your_database;
Database changed
mysql> select id from problems;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
| 4 |
+----+
4 rows in set (0.00 sec)
mysql> select found_rows();
+--------------+
| found_rows() |
+--------------+
| 4 |
+--------------+
1 row in set (0.00 sec)
在mssql中,您可以使用值@@rowcount
。 然后,僅當第一個查詢未返回任何行時,才可以運行第二個查詢:
EXECUTE QUERY;
IF @@rowcount = 0
BEGIN
PREPARE QUERY FROM @querytwo;
EXECUTE QUERY;
END
我最簡單的工作代碼
BEGIN
IF test = 'null' THEN
PREPARE QUERY FROM 'SELECT username as name from login';
EXECUTE QUERY;
ELSE
PREPARE QUERY FROM 'SELECT username as name2 from login';
EXECUTE QUERY;
END IF;
END
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