MySQL explains how it would process the statement, including information about how tables are joined and in which order. For information about using EXPLAIN to obtain execution plan information, see Section 8.8.2, “EXPLAIN Output Format”. 当...
SET return_str =CONCAT(return_str,SUBSTRING(chars_str,FLOOR(1+RAND()*52),1)); SET i = i + 1; END WHILE; RETURN return_str; END // DELIMITER ; 创建存储过程 创建往s1表中插入数据的存储过程: DELIMITER // CREATE PROCEDURE insert_s1 (IN min_num INT (10),IN max_num INT (10)) BE...
('1', substring(cast(3 + (rand() * 10) % 7 AS char(50)), 1, 1), right(left(trim(cast(rand() AS char(50))), 11), 9)); set name = concat(substr(@surname,floor(rand()*length(@surname)/3+1),1), substr(@NAME,floor(rand()*length(@NAME)/3+1),1), substr(@NAME,...
WHILE len>0DOSETfname=CONCAT(fname,SUBSTRING(chars,FLOOR(1+RAND()*62),1));SETlen=len-1;ENDWHILE;SETlen=FLOOR(1+RAND()*25);SETlname=''; WHILE len>0DOSETlname=CONCAT(lname,SUBSTR(chars,FLOOR(1+RAND()*62),1));SETlen=len-1;ENDWHILE;INSERTINTOpersonVALUES(id,fname,lname,FLOOR(...
17 SET return_str = CONCAT(return_str, SUBSTRING(first_name, FLOOR(1 + RAND() * first_name_length), 1)); 18 END IF; 19 20 RETURN return_str; 21END 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. ...
首先这个子查询不是相关子查询,那么这个sql能不能优化成表连接的sql呢? select * from s1 INNER JOIN s2 on s1.key1 = s2.key1 答案是不能,这两个sql是不同的:比如s1表中有一个key1值,s2表有两个重复的key1值,则第一条语句由于是in,所以只会匹配一次,而第二条sql是等于号,所以这种情况下会匹配两次...
(n INT)RETURNS VARCHAR(255) #该函数会返回一个字符串BEGINDECLARE chars_str VARCHAR(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ';DECLARE return_str VARCHAR(255) DEFAULT '';DECLARE i INT DEFAULT 0;WHILE i < n DOSET return_str =CONCAT(return_str,SUBSTRING(chars_str,FLOOR...
( 100 ) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'; DECLARE return_str VARCHAR ( 255 ) DEFAULT ''; DECLARE i INT DEFAULT 0; WHILE i < n DO SET return_str = concat(return_str, SUBSTRING(chars_str, FLOOR( 1 + RAND() * 62 ), 1 )); SET i = i + 1;...
SET return_str =CONCAT(return_str,SUBSTRING(chars_str,FLOOR(1+RAND()*52),1)); SET i = i + 1; END WHILE; RETURN return_str; END // DELIMITER ; SET GLOBAL log_bin_trust_function_creators=1; #创建存储过程: DELIMITER // CREATE PROCEDURE insert_s1 (IN min_num INT (10),IN max_nu...
(n INT)RETURNS VARCHAR(255) #该函数会返回一个字符串BEGINDECLARE chars_str VARCHAR(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ';DECLARE return_str VARCHAR(255) DEFAULT '';DECLARE i INT DEFAULT 0;WHILE i < n DOSET return_str =CONCAT(return_str,SUBSTRING(chars_str,FLOOR...