添加 '数据库/sql基础.md'

数据库/sql基础.md

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+## 1. 创建表
+```sql
+create table ttt(
+    no int primary key,
+    name char(10) not null,
+    depno int,
+    indate date,
+    sal numeric(8,2)
+);
+// numrtic(a,b): 数字类型，总位数为8，小数点后b位
+// char(a): 定长为a的字符串
+// varchar(a): 变长字符串，最大长度为a
+```
+## 2. 删除表
+```sql
+drop table ttt;
+drop table ttt if exists;
+```
+
+## 3. 插入
+```sql
+insert into ttt values(1,"ttt",1,"2023-05-28",12.33);
+insert into ttt(no,name,depno,indate,sal) values(1,"ttt",1,"2023-05-28",12.33);
+insert into ttt(no,name,depno) values(1,"ttt",1);
+```
+
+## 4. distinct去除重复
+```sql
+selet distinct depno from ttt;
+```
+## 5.查询多个值
+```sql
+select name from ttt where depno in (2,3,5);
+select name from ttt where depno not in (2,3,5);
+```
+
+## 6. between
+```sql
+select name from ttt where indate between '2022-01-22' and '2023-04-30';
+// 等价
+select name from ttt where indate>='2022-01-22' and indate<>='2023-04-30';
+
+select name from ttt where indate not between '2022-01-22' and '2023-04-30';
+```