cockroach官方文档翻译---1.3 学习cockroachSQL

1.3学习cockroachSQL

1.3.1 关键的sql语句：

cockroachDB支持标准的SQL延伸，但是一些标准的SQL函数还不可用，详细清查看Sql 特点支持页面，查看更多细节

**创建数据库
cockroah自带单一的默认系统数据库，包含cockroachDB的元数据是只读的

root@:26257/> create database bank;

数据库命名必须遵从这些规则:
https://www.cockroachlabs.com/docs/stable/keywords-and-identifiers.html#identifiers

即：
1）以unicode字母或者下划线开头，后面的字母可以是字母、下划线、数字(0-9)、美元($)
2) 不能使用SQL关键字

root@:26257/> create database bank;

避免数据库存在，可以使用如下语句
----数据库已经存在，也不会有提醒，输出如下

root@:26257/> create database if not exists bank;
CREATE DATABASE
Time: 5.798442ms

删除数据库和其中的所有对象：
root@:26257/> drop database bank;

**查看数据库

Time: 9.822993ms

**设置默认数据库：
root@:26257/> show database
-> ;
+----------+
| database |
+----------+
| |
+----------+
(1 row)

Time: 2.163744ms

设置默认数据库，不需要明确的引用
root@:26257/> set database = bank;
SET

Time: 5.578012ms

查看默认数据库
root@:26257/bank> SHOW database;
+----------+
| database |
+----------+
| bank |
+----------+
(1 row)

Time: 2.164562ms

**创建一个表
root@:26257/> create table bank.accounts(id int primary key,balance decimal);
CREATE TABLE

Time: 49.272314ms
定义数据类型和约束，
数据类型：https://www.cockroachlabs.com/docs/stable/data-types.html
约束： https://www.cockroachlabs.com/docs/stable/constraints.html

当你没有显示的定义一个主键，cochroach会西东定义一个隐藏的rowid作为主键root@:26257/bank> create table if not exists accounts(
-> id int primary key,
-> balance decimal);
CREATE TABLE

Time: 24.13113ms

查看表中的所有列：root@:26257/bank> show columns from accounts;
+---------+---------+-------+---------+-------------+
| Field | Type | Null | Default | Indices |
+---------+---------+-------+---------+-------------+
| id | INT | false | NULL | {"primary"} |
| balance | DECIMAL | true | NULL | {} |
+---------+---------+-------+---------+-------------+
(2 rows)

Time: 39.56398ms

删除表及数据:
root@:26257/bank> drop table accounts;

**查看table
root@:26257/bank> show tables;
+----------+
| Table |
+----------+
| accounts |
+----------+
(1 row)

Time: 8.02106ms

查看其他数据库的表
root@:26257/bank> show tables from animals;
+-------+
| Table |
+-------+
| frogs |
+-------+
(1 row)

Time: 9.405729ms

**插入行

root@:26257/> insert into bank.accounts values (1,1000.50) ;
INSERT 1

乱序插入：
root@:26257/bank> INSERT INTO accounts(balance, id) VALUES (25000.00, 3);
INSERT 1

Time: 13.715741ms

插入多行:
root@:26257/bank> insert into accounts values (4,8100.73),(5,9400.10);
INSERT 2

Time: 13.452986ms

默认值使用,本例子中默认值为空

root@:26257/bank> insert into accounts (id) values (7);
INSERT 1

Time: 40.842133ms

root@:26257/bank> insert into accounts (id,balance) values (6,default);
INSERT 1

Time: 8.194243ms

root@:26257/bank> select * from accounts where id in (6,7);
+----+---------+
| id | balance |
+----+---------+
| 6 | NULL |
| 7 | NULL |
+----+---------+
(2 rows)

Time: 3.471182ms

**创建索引：
索引帮助去定位数据，而不需要去扫描表内的每行数据，自动创建表的主键，有独立约束。

为非唯一列创建索引：
root@:26257/bank> create index balance_idx on accounts(balance desc);
CREATE INDEX

Time: 637.757236ms

在表创建中，可以使用索引
root@:26257/bank> create table custom(id int,name string,index name_idx(name desc));
CREATE TABLE

Time: 49.841363ms

**查看索引

Time: 17.100527ms

**查询数据

root@:26257/bank> select balance from accounts;
+----------+
| balance |
+----------+
| 1000.50 |
| 800.50 |
| 25000.00 |
| 8100.73 |
| 9400.10 |
| NULL |
| NULL |
+----------+
(7 rows)

Time: 7.391805ms

root@:26257/bank> select * from accounts;
+----+----------+
| id | balance |
+----+----------+
| 1 | 1000.50 |
| 2 | 800.50 |
| 3 | 25000.00 |
| 4 | 8100.73 |
| 5 | 9400.10 |
| 6 | NULL |
| 7 | NULL |
+----+----------+
(7 rows)

Time: 6.413298ms

root@:26257/bank> SELECT * FROM accounts where balance >9000;
+----+----------+
| id | balance |
+----+----------+
| 3 | 25000.00 |
| 5 | 9400.10 |
+----+----------+
(2 rows)

Time: 4.9048ms

root@:26257/bank> SELECT * FROM accounts order by balance desc;
+----+----------+
| id | balance |
+----+----------+
| 3 | 25000.00 |
| 5 | 9400.10 |
| 4 | 8100.73 |
| 1 | 1000.50 |
| 2 | 800.50 |
| 6 | NULL |
| 7 | NULL |
+----+----------+
(7 rows)

Time: 4.358385ms

**更新行

root@:26257/bank> update accounts set balance = balance - 5.50 where balance < 10000;
UPDATE 4

Time: 74.469221ms

root@:26257/bank> select * from accounts;
+----+----------+
| id | balance |
+----+----------+
| 1 | 995.00 |
| 2 | 795.00 |
| 3 | 25000.00 |
| 4 | 8095.23 |
| 5 | 9394.60 |
| 6 | NULL |
| 7 | NULL |
+----+----------+
(7 rows)

Time: 6.937405ms
如果一个表有主键，可以使用where子句去更新具体的行，否则每个行匹配到where字句会被更新。

**删除表

root@:26257/bank> delete from accounts where id in (6,7);
DELETE 2

Time: 42.058324ms

root@:26257/bank> select * from accounts;
+----+----------+
| id | balance |
+----+----------+
| 1 | 995.00 |
| 2 | 795.00 |
| 3 | 25000.00 |
| 4 | 8095.23 |
| 5 | 9394.60 |
+----+----------+
(5 rows)

Time: 2.664848ms