MySQL - database query - condition query

Conditions of the query

We know from MySQL Used in table SELECT Statement to query data , To conditionally select data from a table , Can be WHERE Clause to SELECT In the sentence .

grammar

SELECT  Field name  FROM  Table name  WHERE  Conditions ;

Operator table

BETWEEN Followed by the minimum value ,AND Followed by the maximum , It represents an interval , It contains the maximum value and the minimum value

IN(...) If the value we need is in parentheses, it means it is true

LIKE Fuzzy matching , Wildcards are required , One is _  To match a single character , The other is % Means to match any character

IS[NOT] NULL Judge whether a field is empty

Query requirement

1. Inquiry salary is equal to 3000 The employees'

SELECT * FROM emp WHERE sal=3000;

2. Query salary less than 1000 The employees'

SELECT * FROM emp WHERE sal<1000;

3. Query salary less than or equal to 1000 The employees'

SELECT * FROM emp WHERE sal<=1000;

4. Query employees without bonus

SELECT * FROM emp WHERE emp.comm IS NULL;

5. Query employees with bonuses

SELECT * FROM emp WHERE emp.comm IS NOT NULL;

6. Check salary at 1200 To 1800 Employees between ( contain 1200 and 1800)

SELECT * FROM emp WHERE sal>=1200 && sal<=1800;

SELECT * FROM emp WHERE sal>=1200 AND sal<=1800;

SELECT * FROM emp WHERE sal BETWEEN 1200 AND 1800;

7. The inquiry position is salesman , And the salary is less than 1500 The employees'

SELECT * FROM emp WHERE job='salesman' AND sal<1500;

8. Query salary as 800 or 3000 or 5000 The employees'

SELECT * FROM emp WHERE sal=800 OR sal=3000 OR sal=5000;

SELECT * FROM emp WHERE sal in(800,3000,5000);

9. Query employees whose names are four words wildcard Fuzzy query

SELECT * FROM emp WHERE ename LIKE '____';

10. The last person to query the name is S The employees' wildcard % Match any number of

SELECT * FROM emp WHERE ename LIKE '%S';