Data Query: SELECT, FROM, WHERE with relational operators

SQL select command Expplain with example 

Here's a breakdown of a SQL SELECT query, covering the essential components you mentioned: 

Basic Structure of a SELECT Query  

A basic SELECT statement has three main parts:      

SELECT: Used to choose the columns.     

FROM: Specifies the table.     

WHERE: Adds conditions to filter the data.  

sql  SELECT column1, column2, ... FROM table_name WHERE condition;  

Using Relational Operators  Relational operators are used to compare column values:      

• = (equal)     
• != or <> (not equal)     
• > (greater than)     
• < (less than)     
• >= (greater than or equal to)     
• <= (less than or equal to)  

Example:  sql  SELECT name, age FROM employees WHERE age > 30;  

Using BETWEEN  The BETWEEN operator filters results within a specified range.  

sql  SELECT name, salary FROM employees WHERE salary BETWEEN 30000 AND 50000;  

Using Logical Operators  Logical operators are used to combine multiple conditions:      

AND: All conditions must be true.     

OR: At least one condition must be true.     

NOT: Reverses the condition.  

Example:  sql  SELECT name, department FROM employees WHERE age > 25 AND department = 'Sales';  

Using IS NULL and IS NOT NULL  These operators filter rows with NULL (missing) or non-NULL values.  

sql  SELECT name, phone FROM employees WHERE phone IS NULL;  

Or to find non-null values:  

sql  SELECT name, phone FROM employees WHERE phone IS NOT NULL;  

Full Query Example  Combining all of the above:  

sql  SELECT name, department, salary FROM employees WHERE department = 'Sales'   AND salary BETWEEN 30000 AND 50000   AND phone IS NOT NULL;