database cluster: a collection of databases managed by a single PostgreSQL server instance

事务(transaction)原子性:from the point of view of other transactions, it either happens completely or not at all. 以下transaction(Alice转账100给Bob),要么都成功,要么失败:

UPDATE accounts SET balance = balance - 100.00    WHERE name = 'Alice';UPDATE accounts SET balance = balance + 100.00    WHERE name = 'Bob';

标识符(identifier)如果打了双引号,整个引号内视为标识符

UPDATE "my_table" SET "a" = 5;

Key words and unquoted identifiers are case insensitive (都会被理解为小写,比如标识符 FOO, foo, "foo"其实是被解释为同一个.但是"FOO"≠"foo")

UPDATE MY_TABLE SET A = 5;can equivalently be written as:uPDaTE my_TabLE SeT a = 5;因此建议是总是打引号

SQL中的常量

1.用单引号' '引用2.C-style Escapes: 不支持0x00的转义(即,不能出现Null字符 E'0',不代表不能使用Null Value):

mydb=> SELECT E'asd\0asd';ERROR:  invalid byte sequence for encoding "UTF8": 0x00

3.Unicode Escapes:

\四位十六进制(four-digit hexadecimal code) or \+六位十六进制.如果不想用 '\' ,可以 用UESCAPE来替换

U&'d\0061t\+000061'    表示'data'U&'d!0061t!+000061' UESCAPE '!'

4.Dollar-quoted String Constants:

为了更readable,PostgreSQL使用$SomeTag$引用 (注:是用来生成常量的,不是用来写标识符的)

$$Dianne's horse$$$SomeTag$Dianne's horse$SomeTag$

注释

-- This is a standard SQL comment

Alternatively, C-style block comments can be used:

/* multiline comment * with nesting: /* nested block comment */ */