SQL Syntax Reference

Source: Internet
Author: User
Tags create index
I. Data definition DDL (data definition Language)
Data-setting language refers to the language defined in the format and form of data, he is the first to be set up when each database is to be established, what is the form of data, the form of a field key, tables and tables of the relationship between the reference and so on, are in the beginning must be planned.
1, build the form:
CREATE TABLE table_name (
COLUMN1 datatype [NOT NULL] [NOT NULL primary key],
COLUMN2 datatype [NOT NULL],
... )
DataType--is the format of the data, as detailed in the table.
Nut null--Can you allow the data to be empty (no data has been filled in yet).
Primary key--is the primary key for this table.
2. Change the form
Add Column column_name datatype
Description: Adds a field (without deleting a field's syntax.)
Add primary key (column_name)
Description: Change the definition of a table to set a field as the primary key.
Drop primary KEY (column_name)
Description: Delete the definition of the primary key.
3, the establishment of the index
CREATE INDEX index_name on table_name (column_name)
Description: Index The field of a table to increase the speed of the query.
4, delete
Drop table_name
Drop Index_name
Second, the data form datatypes
A 16-bit integer.
A 32-bit integer.
Decimal (P,s)
P exact value and s size decimal integer, the exact value P refers to the total number of values (digits) size value, S is the decimal
There are several numbers after the point. If not specifically specified, the system is set to p=5; S=0.
A 32-bit real number.
A 64-bit real number.
CHAR (n)
N-length string, n cannot exceed 254.
A string whose length is not fixed and its maximum length is n, which cannot exceed 4000.
Graphic (n)
Same as char (n), but its unit is two characters Double-bytes and N cannot exceed 127. This form is for
A font that supports two character lengths, such as Chinese text.
Vargraphic (N)
A two-character string with a variable length and a maximum length of n, and N cannot exceed 2000.
Contains the year, month, and date.
Contains the hours, minutes, and seconds.
Includes year, month, day, time, minutes, seconds, 1 per thousand seconds.
Iii. Data manipulation DML (data manipulation language)
After the data is defined, the next thing is the operation of the data. The operation of the data is nothing more than the addition of data (insert), query data (query), change data (update), delete data (delete) four modes, the following describes their syntax:

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