如果pos存在,返回 substr 在 str 第pos个位置后第一次出现的位置,如果 substr 在 str 中不存在,返回值为0。 SELECT `column` FROM `table` WHERE LOCATE('keyword', `field`)>0 备注:keyword是要搜索的内容,field为被匹配的字段,查询出所有存在keyword的数据 5.2 FIND_IN_SET(str1,str2)方法 返回str2中...
In older MySQL releases, extended information was produced usingEXPLAIN EXTENDED. That syntax is still recognized for backward compatibility but extended output is now enabled by default, so the EXTENDED keyword is superfluous and deprecated. Its use results in a warning; expect it to be removed fr...
// 创建大表 create table bigtable(id bigint, t bigint, uid string, keyword string, url_rank int, click_num int, click_url string) row format delimited fields terminated by '\t'; // 创建小表 create table smalltable(id bigint, t bigint, uid string, keyword string, url_rank int, c...
(1)When youprecede a SELECT statement with the keyword EXPLAIN, MySQL displays informationfrom the optimizer about the query execution plan. That is, MySQL explains howit would process the statement, including information about how tables are joinedand in which order. EXPLAIN EXTENDED can be used ...
// 创建大表create table bigtable(id bigint, t bigint, uid string, keyword string,url_rank int, click_num int, click_url string) row format delimitedfields terminated by '\t';// 创建小表create table smalltable(id bigint, t bigint, uid string, keyword string,url_rank int, click_num...
The EXPLAIN command in PostgreSQL is an essential tool for analyzing and optimizing SQL queries. By providing insights into the query execution plan, EXPLAIN shows how PostgreSQL processes a query, helping identify performance bottlenecks and inefficiencies. When combined with the ANALYZE keyword, EXPLAIN...
create table jointable(id bigint, t bigint, uid string, keyword string, url_rank int, click_num int, click_url string) row format delimited fields terminated by '\t'; 2)分别向大表和小表中导入数据 hive (default)> load data local inpath '/opt/module/data/bigtable' into ...
When theEXTENDED keyword is used, EXPLAIN produces extra information that can be viewedby issuing a SHOW WARNINGS statement following the EXPLAIN statement. Thisinformation displays how the optimizer qualifies table and column names in theSELECT statement, what the SELECT looks like after the applicatio...
in的使用,在没有必要的情况下尽量不要用它,效率很低 or的使用,也尽量不要使用,某些情况下用union效果可能更好.因为使用or的时候可能放弃使用索引 like的使用,尽量不要使用"%%",mysql只能一个个去匹配了...要优化,就要干掉它 人家做搜索引擎的是专业的,数据库做模糊查询,真的没办法.select...
1 row in set (0.00 sec) 一.OptimizingQueries with EXPLAIN The EXPLAINstatement can be used either as a way to obtain information about how MySQLexecutes a statement, or as a synonym for DESCRIBE: (1)When youprecede a SELECT statement with the keyword EXPLAIN, MySQL displays informationfrom ...