mysql 查询语句 过滤_MySQL全面瓦解7：查询的过滤条件
概述
在實際的業務場景應用中，我們經常要根據業務條件獲取并篩選出我們的目標數據。這個過程我們稱之為數據查詢的過濾。而過濾過程使用的各種條件(比如日期時間、用戶、狀態)是我們獲取精準數據的必要步驟，
這樣才能得到我們期望的結果。所以本章我們來學習MySQL中查詢過濾條件的各種用法。
關系運算
關系運算就是where語句后跟上一個或者n個條件，滿足where后面條件的數據會被返回，反之不滿足的就會被過濾掉。operators指的是運算符 ，有如下幾種情況：
運算符
說明
=
等于
<> 或者 !=
不等于
>
大于
>=
大于等于
<
小于
<=
小于等于
關系運算基本的語法格式如下:
1 select cname1,cname2,... from tname where cname operators cval
等于=
查詢出 列和后面的值嚴格相等的數據，非值類型的需要對后面值加上引號，值類型的不需要。
語法格式如下：
1 select cname1,cname2,... from tname where cname = cval;
1 mysql> select * fromuser2;2 +----+-------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+-------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 +----+-------+-----+----------+-----+
9 3 rows in set
10
11 mysql> select * from user2 where name='helen';12 +----+-------+-----+----------+-----+
13 | id | name | age | address | sex |
14 +----+-------+-----+----------+-----+
15 | 2 | helen | 20 | quanzhou | 0 |
16 +----+-------+-----+----------+-----+
17 1 row in set
18
19 mysql> select * from user2 where age=21;20 +----+-------+-----+---------+-----+
21 | id | name | age | address | sex |
22 +----+-------+-----+---------+-----+
23 | 1 | brand | 21 | fuzhou | 1 |
24 | 3 | sol | 21 | xiamen | 0 |
25 +----+-------+-----+---------+-----+
26 2 rows in set
不等于(<>、!=)
不等于有兩種寫法，一種是<>，另一種是!=，意思一樣，可隨意切換使用，但是 <> 先于 != 出現，所以看很多以前的例子，<> 出現頻率比較高，可移植性更強，推薦使用。
不等于的目的是查詢出與條件不符和結果，格式如下：
select cname1,cname2,... from tname where cname <>cval;
或select cname1,cname2,... from tname where cname != cval;
1 mysql> select * fromuser2;2 +----+-------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+-------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 +----+-------+-----+----------+-----+
9 3 rows in set
10
11 mysql> select * from user2 where age<>20;12 +----+-------+-----+---------+-----+
13 | id | name | age | address | sex |
14 +----+-------+-----+---------+-----+
15 | 1 | brand | 21 | fuzhou | 1 |
16 | 3 | sol | 21 | xiamen | 0 |
17 +----+-------+-----+---------+-----+
18 2 rows in set
大于小于(>
一般用于數值或者日期、時間類型的比較，格式如下：
1 select cname1,cname2,... from tname where cname >cval;2
3 select cname1,cname2,... from tname where cname
5 select cname1,cname2,... from tname where cname >=cval;6
7 select cname1,cname2,... from tname where cname <= cval;
1 mysql> select * from user2 where age>20;2 +----+-------+-----+---------+-----+
3 | id | name | age | address | sex |
4 +----+-------+-----+---------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 3 | sol | 21 | xiamen | 0 |
7 +----+-------+-----+---------+-----+
8 2 rows in set
9
10 mysql> select * from user2 whereage>=20;11 +----+-------+-----+----------+-----+
12 | id | name | age | address | sex |
13 +----+-------+-----+----------+-----+
14 | 1 | brand | 21 | fuzhou | 1 |
15 | 2 | helen | 20 | quanzhou | 0 |
16 | 3 | sol | 21 | xiamen | 0 |
17 +----+-------+-----+----------+-----+
18 3 rows in set
19
20 mysql> select * from user2 where age<21;21 +----+-------+-----+----------+-----+
22 | id | name | age | address | sex |
23 +----+-------+-----+----------+-----+
24 | 2 | helen | 20 | quanzhou | 0 |
25 +----+-------+-----+----------+-----+
26 1 row in set
27
28 mysql> select * from user2 where age<=21;29 +----+-------+-----+----------+-----+
30 | id | name | age | address | sex |
31 +----+-------+-----+----------+-----+
32 | 1 | brand | 21 | fuzhou | 1 |
33 | 2 | helen | 20 | quanzhou | 0 |
34 | 3 | sol | 21 | xiamen | 0 |
35 +----+-------+-----+----------+-----+
36 3 rows in set
邏輯運算
運算符說明
AND
多個條件都成立
OR
多個條件中滿足一個
NOT
對條件進行取非操作
AND(且)
當需要多個條件進行數據過濾的時候，使用這種方式，and的每個表達式都是要成立，過濾出來的數據就是用戶需要的。
下面過濾出年齡和性別兩個條件都成立的數據，語法格式如下：
1 select cname1,cname2,... from tname where cname1 operators cval1 and cname2 operators cval2
1 mysql> select * fromuser2;2 +----+-------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+-------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 +----+-------+-----+----------+-----+
10 4 rows in set
11
12 mysql> select * from user2 where age >20 and sex=1;13 +----+-------+-----+---------+-----+
14 | id | name | age | address | sex |
15 +----+-------+-----+---------+-----+
16 | 1 | brand | 21 | fuzhou | 1 |
17 | 4 | weng | 33 | guizhou | 1 |
18 +----+-------+-----+---------+-----+
19 2 rows in set
OR(或)
當多個條件中只要滿足一個條件即進行數據過濾。
下面條件過濾出年齡大于21歲和小于21歲的數據，語法格式如下：
1 select cname1,cname2,... from tname where cname1 operators cval1 or cname2 operators cval2
1 mysql> select * fromuser2;2 +----+-------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+-------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 +----+-------+-----+----------+-----+
10 4 rows in set
11
12 mysql> select * from user2 where age>21 or age<21;13 +----+-------+-----+----------+-----+
14 | id | name | age | address | sex |
15 +----+-------+-----+----------+-----+
16 | 2 | helen | 20 | quanzhou | 0 |
17 | 4 | weng | 33 | guizhou | 1 |
18 +----+-------+-----+----------+-----+
19 2 rows in set
NOT(取非)
對某個滿足的條件進行取反，過濾出來的數據就是用戶需要的。
下面過濾不屬于年齡大于20的數據，語法格式如下：
1 select cname1,cname2,... from tname where not(cname operators cval)
1 mysql> select * fromuser2;2 +----+-------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+-------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 +----+-------+-----+----------+-----+
10 4 rows in set
11
12 mysql> select * from user2 where not(age>20);13 +----+-------+-----+----------+-----+
14 | id | name | age | address | sex |
15 +----+-------+-----+----------+-----+
16 | 2 | helen | 20 | quanzhou | 0 |
17 +----+-------+-----+----------+-----+
18 1 row in set
模糊匹配
就像我們上面的那個用戶表信息表(包含名稱、年齡、地址、性別)，當我們要查詢名稱為s開頭的用戶時，就可以用到 like 關鍵字了，他用以模糊匹配數據。
語法格式如下,pattern中可以包含通配符，有兩種。%：表示匹配任意一個或n個字符； _：表示匹配任意一個字符。
1 select cname1,cname2,... from tname where cname like pattern;
%的使用
1 mysql> select * fromuser2;2 +----+--------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+--------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 | 5 | selina | 25 | taiwang | 0 |
10 +----+--------+-----+----------+-----+
11 5 rows in set
12
13 mysql> select * from user2 where name like 's%';14 +----+--------+-----+---------+-----+
15 | id | name | age | address | sex |
16 +----+--------+-----+---------+-----+
17 | 3 | sol | 21 | xiamen | 0 |
18 | 5 | selina | 25 | taiwang | 0 |
19 +----+--------+-----+---------+-----+
20 2 rows in set
_的使用
1 mysql> select * fromuser2;2 +----+--------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+--------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 | 5 | selina | 25 | taiwang | 0 |
10 +----+--------+-----+----------+-----+
11 5 rows in set
12
13 mysql> select * from user2 where name like 's_l';14 +----+------+-----+---------+-----+
15 | id | name | age | address | sex |
16 +----+------+-----+---------+-----+
17 | 3 | sol | 21 | xiamen | 0 |
18 +----+------+-----+---------+-----+
19 1 row in set
注意點
1、不要過度使用模糊匹配得通配符。如果其他操作符能達到相同的目的，應該使用其他操作符
2、對大體量的表進行模糊匹配的時候盡量不要以%開頭，比如 like '%username',這樣會執行掃表，效率較慢。盡量明確模糊查找的開頭部分，比如 like 'brand%'，會先定位到brand開頭的數據，效率高很多。
范圍值檢查
BETWEEN AND(區間查詢)
操作符 BETWEEN … AND 會選取介于兩個值之間的數據范圍，這些值可以是數值、文本或者日期，屬于一個閉區間查詢。
and 的左邊val1 和 右邊 val2 分別表示兩個臨界值，等同于數學公式[val1,val2] ，屬于這兩個區間的數據會被過濾出來(>=val1 和 <=val2),所以語法格式如下：
1 selec cname1,cname2,... from tname where cname between val1 andval2;2 等同于3 selec cname1,cname2,... from tname where cname >= val1 and cname <= val2;
查詢年齡在[21,25]之間的數據：
1 mysql> select * fromuser2;2 +----+--------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+--------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 | 5 | selina | 25 | taiwang | 0 |
10 +----+--------+-----+----------+-----+
11 5 rows in set
12
13 mysql> select * from user2 where age between 21 and 25;14 +----+--------+-----+---------+-----+
15 | id | name | age | address | sex |
16 +----+--------+-----+---------+-----+
17 | 1 | brand | 21 | fuzhou | 1 |
18 | 3 | sol | 21 | xiamen | 0 |
19 | 5 | selina | 25 | taiwang | 0 |
20 +----+--------+-----+---------+-----+
21 3 rows in set
22
23 mysql> select * from user2 where age >= 21 and age <= 25;24 +----+--------+-----+---------+-----+
25 | id | name | age | address | sex |
26 +----+--------+-----+---------+-----+
27 | 1 | brand | 21 | fuzhou | 1 |
28 | 3 | sol | 21 | xiamen | 0 |
29 | 5 | selina | 25 | taiwang | 0 |
30 +----+--------+-----+---------+-----+
31 3 rows in set
IN(包含查詢)
按照上面得數據，如果我們想查出居住地位于福州和廈門得用戶數據，應該使用 IN操作符，因為 IN 操作符允許我們在 WHERE 子句中指定多個值，符合這些值中得某一項，既滿足條件返回數據。
語法格式如下，in 后面列表的值類型必須一致或兼容，且不支持通配符：
1 select cname1,cname2,... from tname where cname in (val1,val2,...);
1 mysql> select * fromuser2;2 +----+--------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+--------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 | 5 | selina | 25 | taiwang | 0 |
10 +----+--------+-----+----------+-----+
11 5 rows in set
12
13 mysql> select * from user2 where address in('fuzhou','xiamen');14 +----+-------+-----+---------+-----+
15 | id | name | age | address | sex |
16 +----+-------+-----+---------+-----+
17 | 1 | brand | 21 | fuzhou | 1 |
18 | 3 | sol | 21 | xiamen | 0 |
19 +----+-------+-----+---------+-----+
20 2 rows in set
NOT IN(對包含查詢取反)
我們上面已經學習過了not得用戶，對not后面執行得表達式進行取反得操作，測試下：
1 mysql> select * fromuser2;2 +----+--------+-----+----------+-----+
3 | id | name | age | address | sex |
4 +----+--------+-----+----------+-----+
5 | 1 | brand | 21 | fuzhou | 1 |
6 | 2 | helen | 20 | quanzhou | 0 |
7 | 3 | sol | 21 | xiamen | 0 |
8 | 4 | weng | 33 | guizhou | 1 |
9 | 5 | selina | 25 | taiwang | 0 |
10 +----+--------+-----+----------+-----+
11 5 rows in set
12
13 mysql> select * from user2 where address not in('fuzhou','quanzhou','xiamen');14 +----+--------+-----+---------+-----+
15 | id | name | age | address | sex |
16 +----+--------+-----+---------+-----+
17 | 4 | weng | 33 | guizhou | 1 |
18 | 5 | selina | 25 | taiwang | 0 |
19 +----+--------+-----+---------+-----+
20 2 rows in set
空值檢查
IS NULL/IS NOT NULL
判斷是否為空，語法格式如下，這邊注意的是，對值為null的數據，各種比較運算符、like、between and、in、not in查詢都不起作用，只有is null 能夠過濾出來。
1 select cname1,cname2,... from tname where cname is null;2 或者3 select cname1,cname2,... from tname where cname is not null;
1 mysql> select * from user2 where address is null;2 +----+--------+-----+---------+-----+
3 | id | name | age | address | sex |
4 +----+--------+-----+---------+-----+
5 | 5 | selina | 25 | NULL | 0 |
6 +----+--------+-----+---------+-----+
7 1 row in set
8
9 mysql> select * from user2 where address is not null;10 +----+-------+-----+----------+-----+
11 | id | name | age | address | sex |
12 +----+-------+-----+----------+-----+
13 | 1 | brand | 21 | fuzhou | 1 |
14 | 2 | helen | 20 | quanzhou | 0 |
15 | 3 | sol | 21 | xiamen | 0 |
16 | 4 | weng | 33 | guizhou | 1 |
17 +----+-------+-----+----------+-----+
18 4 rows in set
有一種關鍵字 <=>，可以包含對null值得判斷，但是目前用的比較少了，有興趣可以去查查，這邊不贅述。
總結
1、like表達式中的%匹配一個到多個任意字符，_匹配一個任意字符
2、空值查詢需要使用IS NULL或者IS NOT NULL，其他查詢運算符對NULL值無效。即使%通配符可以匹配任何東西，也不能匹配值NULL的數據。
3、建議創建表的時候，表字段不設置空，給字段一個default 默認值。
4、MySQL支持使用NOT對IN 、BETWEEN 和EXISTS子句取反 。
總結
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