MySQL學習-SQL語句的分類與MySQL簡單查詢
1.SQL語句的分類
學習MySQL主要還是學習通用的SQL語句,那麼SQL語句包括增刪改查,SQL語句怎麼分類呢?
DQL(資料查詢語言): 查詢語句,凡是select語句都是DQL。
DML(資料操作語言):insert delete update,對錶當中的資料進行增刪改。
DDL(資料定義語言):create drop alter,對錶結構的增刪改。
TCL(事務控制語言):commit提交事務,rollback回滾事務。(TCL中的T是Transaction)
DCL(資料控制語言): grant授權、revoke撤銷許可權等。
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注:下面所示案例中所用到的資料庫均在本頁的末尾:
2.簡單查詢
操作的表
mysql> select * from emp;
EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
---|---|---|---|---|---|---|---|
7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
其每個欄位的欄位名分別為員工編號、員工姓名、員工職位、員工上級領導編號、員工僱傭日期,員工薪水、員工津貼、員工部門編號。
語法格式:
select 欄位名1,欄位名2,欄位名3,… from 表名;
提示:
1、任何一條sql語句以“;”結尾。
2、sql語句不區分大小寫。
select ename,empno from emp;
注意:如果顯示數量過多,或者顯示的查詢資料的數量無關緊要時,截圖一般只截取了部分。
查詢員工的年薪(欄位可以參與數學運算。)
select ename,sal*12 from emp;
給查詢結果的列重新命名?
select ename,sal * 12 as yearsal from emp;
別名中有中文?
select ename,sal * 12 as 年薪 from emp; // 錯誤
select ename,sal * 12 as ‘年薪’ from emp;
注意:標準sql語句中要求字串使用單引號括起來。雖然mysql支援雙引號,儘量別用。
as關鍵字可以省略?
select empno,ename,sal * 12 yearsal from emp;
查詢所有欄位?
select * from emp;
實際開發中不建議使用,效率較低。
注:本版塊中MySQL所用到的資料庫bjpowernode程式碼如下,可以直接執行生成資料庫檔案
DROP TABLE IF EXISTS EMP;
DROP TABLE IF EXISTS DEPT;
DROP TABLE IF EXISTS SALGRADE;
CREATE TABLE DEPT
(DEPTNO int(2) not null ,
DNAME VARCHAR(14) ,
LOC VARCHAR(13),
primary key (DEPTNO)
);
CREATE TABLE EMP
(EMPNO int(4) not null ,
ENAME VARCHAR(10),
JOB VARCHAR(9),
MGR INT(4),
HIREDATE DATE DEFAULT NULL,
SAL DOUBLE(7,2),
COMM DOUBLE(7,2),
primary key (EMPNO),
DEPTNO INT(2)
)
;
CREATE TABLE SALGRADE
( GRADE INT,
LOSAL INT,
HISAL INT );
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
10, 'ACCOUNTING', 'NEW YORK');
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
20, 'RESEARCH', 'DALLAS');
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
30, 'SALES', 'CHICAGO');
INSERT INTO DEPT ( DEPTNO, DNAME, LOC ) VALUES (
40, 'OPERATIONS', 'BOSTON');
commit;
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7369, 'SMITH', 'CLERK', 7902, '1980-12-17'
, 800, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20'
, 1600, 300, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7521, 'WARD', 'SALESMAN', 7698, '1981-02-22'
, 1250, 500, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7566, 'JONES', 'MANAGER', 7839, '1981-04-02'
, 2975, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28'
, 1250, 1400, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01'
, 2850, NULL, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7782, 'CLARK', 'MANAGER', 7839, '1981-06-09'
, 2450, NULL, 10);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7788, 'SCOTT', 'ANALYST', 7566, '1987-04-19'
, 3000, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7839, 'KING', 'PRESIDENT', NULL, '1981-11-17'
, 5000, NULL, 10);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08'
, 1500, 0, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7876, 'ADAMS', 'CLERK', 7788, '1987-05-23'
, 1100, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7900, 'JAMES', 'CLERK', 7698, '1981-12-03'
, 950, NULL, 30);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7902, 'FORD', 'ANALYST', 7566, '1981-12-03'
, 3000, NULL, 20);
INSERT INTO EMP ( EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM,
DEPTNO ) VALUES (
7934, 'MILLER', 'CLERK', 7782, '1982-01-23'
, 1300, NULL, 10);
commit;
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
1, 700, 1200);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
2, 1201, 1400);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
3, 1401, 2000);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
4, 2001, 3000);
INSERT INTO SALGRADE ( GRADE, LOSAL, HISAL ) VALUES (
5, 3001, 9999);
commit;