Soft test: SQL Server Basic Syntax reference

server| Reference | grammar | Grammar reference

I. Data definition DDL (data definition Language)

Data definition 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],

...)

Description

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

ALTER TABLE TABLE_NAME

Add Column column_name datatype

Description: Adds a field (without deleting a field's syntax.)

ALTER TABLE TABLE_NAME

Add primary key (column_name)

Description: Change the definition of a table to set a field as the primary key.

ALTER TABLE TABLE_NAME

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, data form datatypes

smallint

A 16-bit integer.

Interger

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.

Float

A 32-bit real number.

Double

A 64-bit real number.

CHAR (n)

N-length string, n cannot exceed 254.

VARCHAR (n)

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.

Date

Contains the year, month, and date.

Time

Contains the hours, minutes, and seconds.

Timestamp

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:

1. Additional Information:

INSERT INTO table_name (COLUMN1,COLUMN2,...)

VALUES (value1,value2, ...)

Description

1. If no column system is specified, the information will be filled in the order of the fields in the table.

2. The data form of the field and the information to be filled must match.

3.table_name can also be a landscape view_name.

INSERT INTO table_name (COLUMN1,COLUMN2,...)

Select Columnx,columny,... from another_table

Note: You can also go through a subquery (subquery) to fill in the other forms of information.

2, Inquiry information:

Basic Query

Select Column1,columns2,...

From table_name

Description: List all the specific field data of the TABLE_NAME

SELECT *

From table_name

where Column1 = * * *

[and Column2 > YYY] [or Column3 <> zzz]

Description

1. ' * ' indicates that all of the fields are listed.

The 2.where is followed by a conditional type, which lists the eligible data.

Select Column1,column2

From table_name

ORDER BY Column2 [DESC]

Description: Order BY IS to specify a column to do the sort, [desc] refers to from large to small, if not specified, is small to large

Arranged

Group Query

A combination query means that the source of the query is not only a single form, but a joint of more than one

The form will be able to get the result.

SELECT *

From Table1,table2

where Table1.colum1=table2.column1

Description

1. Query the information in the two tables with the same column1 value.

2. Of course, two tables are compared to each other in a field with the same data form.

3. A complex query may be used in a number of forms.

Consolidated queries:

Select COUNT (*)

From table_name

WHERE column_name = * * *

Description

There are a few strokes of the information that meets the criteria.

Select SUM (column1)

From table_name

Description

1. Calculates the sum, the selected field must be a number shape that can be counted.

2. In addition to AVG () is the calculation of average, Max (), Min () to calculate the maximum minimum value of the integration of the query.

Select Column1,avg (Column2)

From table_name

GROUP BY Column1

Having avg (COLUMN2) > * * *

Description

1.group by: Column1 for a set of column2 average must be the keyword of the consolidated query such as AVG, SUM, etc.

Used together.

2.having: Must be used with group by as a consolidation restriction.

Complex query

SELECT *

From table_name1

where exists (

SELECT *

From Table_name2

where conditions)

Description

The 1.where conditions can be another query.

2.exists here refers to the existence or not.

SELECT *

From table_name1

where Column1 in (

Select Column1

From Table_name2

where conditions)

Description

1. In the back face is a collection that indicates that the COLUMN1 exists within the set.

2. The data form of select must conform to Column1.

Other queries

SELECT *

From table_name1

where column1 like ' x percent '

Description: Like must correspond to the ' x ' of the back side to indicate a string with the beginning of X.

SELECT *

From table_name1

where Column1 in (' * * *, ' yyy ',..)

Description: In the back face is a collection, which means that the column1 exists within the set.

SELECT *

From table_name1

where column1 between XX and yy

Description: Between indicates that the value of Column1 is between XX and yy.

3. Change information:

UPDATE table_name

Set column1= ' * * *

where Conditoins

Description

1. Change a field to set its value to ' * * *.

2.conditions is the condition you want to meet, and if there is no where, the entire table's field will all be changed.

4, delete the information:

Delete from table_name

Where conditions

Note: Delete the eligible information.

Note: There are different expressions for different databases if there is a comparison of dates after the Where condition. Specifically as follows:

(1) In the case of an Access database: where mydate> #2000 -01-01#

(2) If it is an Oracle database: where Mydate>cast (' 2000-01-01 ' as date)

Or: Where Mydate>to_date (' 2000-01-01 ', ' yyyy-mm-dd ')

Written in Delphi:

Thedate= ' 2000-01-01 ';

Query1.sql.add (' SELECT * FROM ABC where mydate>cast (' + ' ' ' +thedate+ ' ' + ' as Date ');

If the date-time type is compared:

where Mydatetime>to_date (' 2000-01-01 10:00:01 ', ' yyyy-mm-dd hh24:mi:ss ')