Data Base and Testing Q & A

Types of SQL Commands:
There are five types of SQL commands: DDL, DML, DCL, TCL, and DQL

BASE QUERY

·    SELECT * FROM
table_name;This query returns every column and every row of the table called table_name.

·    SELECT * FROM table_name LIMIT 10;

It returns every column and the first 10 rows from table_name.

·    SELECTING SPECIFIC COLUMNS

·    SELECT column1, column2, column3 FROM table_name;

This query returns every row of column1, column2 and column3 from table_name

 

DATA TYPES IN SQL
In SQL we have more than 40 different data types. But these seven are the most important ones:

1. Integer. A whole number without a fractional part. E.g. 1, 156, 2012412

2. Decimal. A number with a fractional part. E.g. 3.14, 3.141592654, 961.1241250

3. Boolean. A binary value. It can be either TRUE or FALSE.

4. Date. Speaks for itself. You can also choose the format. E.g. 2017-12-31

5. Time. You can decide the format of this, as well. E.g. 23:59:59

6. Timestamp. The date and the time together. E.g. 2017-12-31 23:59:59

7. Text. This is the most general data type. But it can be alphabetical letters only,

or a mix of letters and numbers and any other characters.