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查询优化__龙腾

ITWYY 2022-05-01 阅读 17

CREATE TABLE t(
	id INT,
	num INT DEFAULT 0,
	NAME VARCHAR(20)
)
 
DELIMITER $
CREATE PROCEDURE t()
BEGIN
DECLARE i INT DEFAULT 0;
DECLARE f INT DEFAULT 1;
WHILE(i<1000) DO
	BEGIN
		SELECT i;
		SELECT f;
		SET i=i+1;
		SET f=f+1;
		INSERT INTO t(id,num)VALUES(f,i);
	END;
END WHILE;
END $
DELIMITER ;
 
CALL t();
 
SELECT * FROM t
 
#创建索引
CREATE INDEX ix_num ON t(num);
 
#使用索引
SELECT id FROM t WHERE num IS NULL
#不使用索引
SELECT id FROM t WHERE num=0;
 
#避免使用!+ 或 <> 符号
SELECT * FROM t WHERE num!=5;
SELECT * FROM t WHERE num<>5;
 
#避免使用or
SELECT id FROM t WHERE num=10 OR num=20;
 
SELECT id FROM t WHERE num=10
UNION
SELECT id FROM t WHERE num=20
 
 
#尽量少用in , not in 使用between
SELECT id FROM t WHERE num IN(1,2,3);
SELECT id FROM t WHERE num BETWEEN 1 AND 3;
 
#模糊查询,字母打头
SELECT * FROM t WHERE NAME LIKE 'a%';
 
#避免索引字段进行函数操作
SELECT id FROM t WHERE SUBSTRING(NAME,1,3)='abc';
SELECT id FROM t WHERE NAME LIKE 'abc%';
 
#复合索引,必须使用第一个字段
CREATE INDEX ix_id_name ON t(id,NAME);
SELECT * FROM t WHERE id =10;
SELECT * FROM t WHERE id=10 AND NAME='li';
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