(1)优化前：使用or的时候，SQL执行时间1.47smysql> select e.emp_no,e.first_name,d.dept_no,d.from_date,d.to_date from employees e left join dept_emp d on e.emp_no=d.emp_no where e.emp_no=32000 or d.from_date=1996-11-24; 58 rows in set (1.47 sec)mysql> desc select e.emp_no,e.first_name,d.dept_no,d.from_date,d.to_date from employees e left join dept_emp d on e.emp_no=d.emp_no where e.emp_no=32000 or d.f...
前提，是每个查询结果集的列数要一样，类型要一样SELECT g.goods_id FROM ( SELECT gr.`GOODS_ID`,COUNT(gr.`GOODS_ID`) num FROM rkgl_goods_repertory gr JOIN rkgl_repertory r ON r.`ID`=gr.`REPERTORY_ID` JOIN spgl_goods g ON g.`ID`=gr.`GOODS_ID` JOIN spgl_brand b ON b.`ID`=g.`BRAND_ID` JOIN spgl_goods_type gt ON gt.`ID`=g.`GOODS_TYPE_ID` WHERE r.`USER_ID`=36 AND g.`IS_DELETE`=FALSE AND gt.`IS_DELETE`=FALS...
我有一些SQL代码,它正是我想要它的工作方式：select 10 as number, "Checklist 10 Foo" as name, max(id), max(ts) as max_ts, callsign, max(time_hint_utc), count(*) from checklist_10 union all select 11 as number, "Checklist 11 Bar" as name, max(id), max(ts) as max_ts, callsign, max(time_hint_utc), count(*) from checklist_11 union all select 12 as number, "Checklist 12 Baz" as name, max(id), max(ts) as m...
16.7 The MERGE Storage Engine 16.7.2 merge table problemsThe MERGE storage engine, also known as the MRG_MyISAM engine, is a collection of identical MyISAM tables that can be used as one. “Identical” means that all tables have identical column data types and index information. You cannot merge MyISAM tables in which the columns are listed in a different order, do not have exactly the same data t...
我是MySQL的新手,需要请求你的帮助.我正在使用不同的WHERE子句值来区分联合的2个部分中的同一个表中的2组计数值;像这样：SELECT Count(column1) as 'RED', null as 'BLUE' FROM TableA Where column1 Like 'RED' UNION SELECT NULL, Count(column1) FROM TableA Where column1 Like 'BLUE'我希望得到：RED BLUE --- ---- 23 55但我真正得到的是：RED BLUE --- ---- 23 NULL NULL 55谁能告诉我...
我有一个联合查询,如下所示：(SELECT t.id, t.name, c.company AS owner, t.creation_date AS date, t.notesFROM tool t, client cWHERE t.id_customer = 15 AND t.trash_flag = 1)UNION (SELECT f.id, f.name, CONCAT(m.first_name, , m.last_name) AS owner, f.date, f.notesFROM file f, meta mWHERE ((f.acl = 0) OR (f.acl = 1 AND 1 = TRUE) OR (f.acl = 2 AND f.id = 7)) AND f.id = 15 AND f.trash_flag = 1 AND m.user_i...
bitsCN.com (参考自<>) 假设有这样的需求：写一个UNION查询，其第一个子查询作为分支先执行，如果找到了匹配的行，则不再执行第二个分支的查询。一般来说，我们可以写出这样的UNION查询:select id from users where id=123456union allselect id from users_archived where id = 123456;此查询可以正常运行，但是无论在users表中是否找到记录，都会到users_archived表中扫描一次；因此可能也会返回重复的记录。为了减少这种情况下不...
UNION的语法结构： SELECT ... UNION [ ALL | DISTINCT ] SELECT .... [ UNION [ ALL | DISTINCT ] SELECT .....] UNION 用于将多个SELECT语句中的结果组合到单个结果集中。 1 第一个SELECT语句用的列名称用作返回结果的列名称其中第一个select中查询的列名为user_name，第二个select中查询的列名为password，但显示的结果列名称只有user_name 在多个select语句中，对应的列应该具有相同的数据类型，如果相应的select猎德数据类型...
在 MySQL UNION 中使用 LIMIT 用于限制返回的记录条数，如果对 SELECT 子句做限制，需要对 SELECT 添加圆括号： (SELECT aid,title FROM article LIMIT 2) UNION ALL (SELECT bid,title FROM blog LIMIT 2)该 SQL 会返回个 SELECT 语句的两条记录，如果不添加圆括号，则最后一个 LIMIT 2 会作用于整个 UNION 语句而一共返回 2 条记录。同 ORDER BY 类似，当需要对整个 UNION 的结果进行 LIMIT 限制时，建议将各个 SELECT 语句用圆...
如何从中获得明显的title.id：SELECT Title.id, Title.title FROM titles as Title HAVING points > 0 UNION ALL SELECT Title.id, Title.title FROM titles as Title HAVING points > 1查询还有更多内容,但这应该足够了.解决方法:只需删除ALL即可.一些风格允许添加DISTINCT而不是ALL更明确,但这是多余的,因为默认值总是过滤我们的重复项. MySQL – http://dev.mysql.com/doc/refman/5.0/en/union.htmlMSSQL – http://msdn.mi...
———————mysql_field_table 是获取数据表名的函数，正常情况下的的sql select 只查询1个表，是可以执行，请问：当sql select在union查询多个表之后，请问怎么样获取多个表名？———————可以执行的代码：//sql select 只查询1条数据 $sql = "SELECT id,title FROM `TABLE1` WHERE id IN($id)ORDER BY id DESCLIMIT 0,10 "; $result = mysql_query($sql); $table_name = mysql_field_table($result,0); echo "表名：$tabl...
我有几个相同结构的表，需要进行联表查询，我使用如下的语句 select sum(cnt) from (select count(*) as cnt from t1 where a>100 union all select ...) as t; 这一句拿总和的挺快。 select * from t1 where a>100 union all select * from t2 where a>100 union all select * from t3 where a>100 order by b desc limit 0,10000; 这一句效率好像很低，等了很久才出来结果。 应该如何优化，谢谢 回复讨...
mysql UNION 有重复的数据，怎么解决？SELECT * , 1 AS xhFROM textWHERE (id AND `title` LIKE '%德国%'AND `title` LIKE '%丹麦%')UNION SELECT * , 2 AS xhFROM textWHERE (id AND `title` LIKE '%德国%'OR `title` LIKE '%丹麦%')ORDER BY xhLIMIT 6------解决方案-------------------- 改成'x''X'.....这么诡异的注意你也能想出来....嗯, 至少要加个注释,要不将来被N个读代码的骂不要怪我.....关于括号: id 相当于 (...
mysql union all 的效率问题 我有几个相同结构的表，需要进行联表查询，我使用如下的语句select sum(cnt) from (select count(*) as cnt from t1 where a>100 union all select ...) as t; 这一句拿总和的挺快。select * from t1 where a>100 union all select * from t2 where a>100 union all select * from t3 where a>100 order by b desc limit 0,10000; 这一句效率好像很低，等了很久才出来结果。应该如何优化，谢谢 ------解...
mysqlthinkphpphpunion 代码$result4=$activity->where("topic=%s and city=%s","top",I(get.city))->field(createTime,title,readCount,id,belong)->table(gq_activity)->union(SELECT createTime,title,readCount,id,belong FROM gq_preferential WHERE topic="top")->union(SELECT createTime,title,readCount,id,belong FROM gq_multimedia WHERE topic="top")->union(SELECT createTime,title,readCou...