Transact-SQL (T-SQL) is the extension of SQL (Structured Query Language) used specifically for Microsoft SQL Server. T-SQL commands are used to interact with SQL Server databases and perform various operations. Here are some common T-SQL commands:
1. **SELECT**: Retrieve data from one or more database tables.
```
SELECT column1, column2, ...
FROM table_name;
```
2. **INSERT**: Insert new records into a table.
```
INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);
```
3. **UPDATE**: Modify existing records in a table.
```
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
```
4. **DELETE**: Remove records from a table.
```
DELETE FROM table_name
WHERE condition;
```
5. **CREATE TABLE**: Create a new database table.
```
CREATE TABLE table_name (
column1 data_type constraint,
column2 data_type constraint,
...
);
```
6. **ALTER TABLE**: Modify an existing table structure.
```
ALTER TABLE table_name
ADD column_name data_type constraint;
ALTER TABLE table_name
ALTER COLUMN column_name data_type;
ALTER TABLE table_name
DROP COLUMN column_name;
```
7. **DROP TABLE**: Delete a table from the database.
```
DROP TABLE table_name;
```
8. **CREATE DATABASE**: Create a new database.
```
CREATE DATABASE database_name;
```
9. **USE**: Switch to a specific database.
```
USE database_name;
```
10. **TRUNCATE TABLE**: Remove all rows from a table, but keep the table structure.
```
TRUNCATE TABLE table_name;
```
11. **JOIN**: Combine rows from two or more tables based on a related column.
```
SELECT column1, column2, ...
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;
```
12. **GROUP BY**: Group rows based on the values of a column.
```
SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1;
```
13. **HAVING**: Filter the results of a GROUP BY clause.
```
SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1
HAVING COUNT(*) > 1;
```
14. **ORDER BY**: Sort the result set in ascending or descending order.
```
SELECT column1, column2, ...
FROM table_name
ORDER BY column1 ASC; -- or DESC for descending order
```
15. **CREATE INDEX**: Create an index on one or more columns to improve query performance.
```
CREATE INDEX index_name
ON table_name (column1, column2, ...);
```
These are some of the fundamental T-SQL commands used to interact with Microsoft SQL Server databases. Keep in mind that there are many other T-SQL commands and functionalities available to manage and query databases efficiently.
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