• where語句（篩選條件）

SELECT * FROM person_sales WHERE grade=3

SELECT * FROM person_sales WHERE grade>3

SELECT * FROM person_sales WHERE sale_amount <= 50000

SELECT * FROM person_sales WHERE grade<>3

SELECT * FROM person_sales WHERE grade!=3

備註：不等於可以用 <> 或 != 表示

SELECT * FROM person_sales WHERE
 
 staff_name='張進'

備註：如果想表示文字內容，必須要加單引號''或雙引號""，將其表示成字串

SELECT * FROM person_sales where grade=3 ORDER BY sale_amount DESC LIMIT 10

備註：順序——select 欄位 FROM表名 where 篩選條件 order by 排序欄位 Limit 記錄數量

SELECT * FROM person_sales where sale_amount=0 ORDER BY grade LIMIT 1

• NULL值的處理

代表該欄位為空，沒有填寫過任何內容（空不是0）

SELECT
 
 * FROM person_sales where sale_amount IS null

備註：判斷空值不能用 =! ，需要用 IS NULL

• 邏輯操作符 and or not

SELECT * FROM gb_members WHERE grade=2 OR grade=3

SELECT * FROM gb_members WHERE grade=3 AND income>2000

SELECT * FROM gb_members 
    WHERE (grade=3 AND income>2900
                OR grade=2 AND income>
 
2950)
            AND kill_enemy>3

備註：（1）邏輯運算優先順序 括號 > not > and > or（2）必須是半形括號（3）只用圓角括號，不能使用方括號、花括號

SELECT * FROM gb_members 
    WHERE NOT((grade=3 AND income>2900
                OR grade=2 AND income>2950)
            AND kill_enemy>3)

SELECT * FROM gb_members 
    WHERE (grade=3 AND income>2900
                OR grade=2 AND income>2950)
            AND kill_enemy>3
            AND (kitchen_skill='白斬雞' OR kitchen_skill='叫花雞')
    ORDER BY income DESC, kill_enemy desc
    LIMIT 10

SELECT * FROM gb_members 
    WHERE (grade=3 AND income>2900
                OR grade=2 AND income>2950)
            AND kill_enemy>3
            AND kitchen_skill IN ('白斬雞','叫花雞')
    ORDER BY income DESC, kill_enemy desc
    LIMIT 10

備註：x in (a,b,c,…) 只要x的值等於括號中任意一項，即視為符合條件，相當於x=a or x=b or x=c