Operátor porovnání SQL

Operátor porovnání porovnává různá data tabulky Structured Query Language a kontroluje, zda jsou data stejná, menší než, větší než, menší nebo větší než stejná. Porovnávací dotaz SQL se používá s klauzulí where ke spuštění dotazů.

Můžeme použít porovnávací operátor s klauzulí WHERE pomocí příkazů SELECT, UPDATE a DELETE ve Structured Query Language.

Existuje několik operátorů porovnání, které se používají k provádění záznamů uložených v tabulce SQL:

1. Operátor SQL Equal (=)
2. Operátor SQL se nerovná (! =)
3. SQL menší než operátor (<)
4. SQL větší než operátor (>)
5. SQL je menší než se rovná operátoru (<=)
6. SQL větší než se rovná operátoru (>=)

Pojďme se hluboce ponořit do POROVNÁVACÍHO OPERÁTORA SQL

Operátor SQL Equal

Operátor Equal je nejčastěji používaný dotaz v SQL dotazech. Tento operátor zobrazí pouze ta data, která odpovídají konkrétním kritériím v dotazu.

Syntaxe pro přístup k datům z tabulky pomocí operátoru EQUAL

SELECT * FROM TABLENAME WHERE column-name = value;

Syntaxe pro aktualizaci dat z tabulky pomocí operátoru EQUAL

UPDATE TABLENAME SET column_name = value WHERE column_name = value;

Syntaxe pro odstranění dat z tabulky pomocí operátoru EQUAL

DELETE FROM TABLENAME WHERE column_name = value;

Pojďme pochopit níže uvedený příklad, který vysvětluje, jak spustit Equal Operator v dotazu SQL:

Zvažte existující tabulky, které mají následující záznamy:

Tabulka:Zaměstnanci

Příklad 1: Napište dotaz pro zobrazení záznamů zaměstnanců z tabulky zaměstnanců, jejichž oddělením zaměstnanců je ‚Oracle‘.

SELECT * FROM EMPLOYEES WHERE DEPARTMENT = 'ORACLE';

Z výše uvedeného dotazu získáváme údaje o zaměstnancích z tabulky zaměstnanců, kde se oddělení zaměstnanců rovná oddělení oracle.

Výstup:

As we can see in the output, only oracle department employees’ records are displayed.

Příklad 2: Write a query to display the employee records from the employees' table whose employee department is 'Oracle' or City is 'Pune'.

SELECT * FROM EMPLOYEES WHERE DEPARTMENT = 'ORACLE' OR CITY = 'PUNE';

From the above query, we are fetching the employee data from the employees' table where the employee department is equal to the oracle department or City is equal to Pune city. The first search will go for the Oracle department as records are done with the Oracle department, then the query will go for Pune city. Here we used multiple Equal operators using OR operator.

Výstup:

As we can see in the output, only oracle department employees' or Pune city records are displayed.

Příklad 3: Write a query to display the employee records from the employees' table whose City is 'Pune' and Salary is 65500.

SELECT * FROM EMPLOYEES WHERE CITY ='PUNE'AND SALARY =65500;

From the above query, we are fetching the employee data from the employees' table where employee city is equal to Pune city, and employee salary is 65500. Here we used multiple Equal operators using AND operator. AND the operator will return only those records whose both conditions are true.

Output:

As we can see in the output, only Pune city and 65500 salary records are displayed.

Příklad 4: Write a query to update the employee records from the employees’ table whose employee department is ‘FMW’.

UPDATE EMPLOYEES SET SALARY = 55500 WHERE DEPARTMENT = 'FMW';

We update the employee records from the above query from the employees' table whose department is FMW.

To cross-check whether the records are updated or not, we will run the SELECT statement.

SELECT * FROM EMPLOYEES WHERE DEPARTMENT = 'FMW';

As we can see, the records are updated successfully; whose department name is FMW.

Příklad 5: Write a query to update the employee records from the employees' table whose employee city is 'Pune' and the department is 'Java'.

UPDATE EMPLOYEES SET SALARY = 60000 WHERE CITY = 'PUNE' AND DEPARTMENT = 'JAVA';

From the above query, we update the employee records from the employees' table whose CityCity is Pune and department is Java.

To cross-check whether the records are updated or not, we will run the SELECT statement.

SELECT * FROM EMPLOYEES WHERE CITY = 'PUNE' AND DEPARTMENT = 'JAVA';

Příklad 6: Write a query to delete the employee records from the employees’ table whose employee id is 5001.

DELETE FROM EMPLOYEES WHERE EMPLOYEEID = 5001;

From the above query, we are deleting the employee records from the employees’ table whose employee id is 5001.

To cross-check whether the record is deleted or not, we will run the SELECT statement.

SELECT * FROM EMPLOYEES;

As we can see, the record of employee id 5001 is deleted successfully.

SQL Not Equal Operator

The Equal Not Operator displays only those records whose values are not similar to the query's specified value.

SQL Not Equal operator returns those data from the table if the value doesn’t meet the criteria in the given query.

Syntax to access data from the table using the NOT EQUAL operator

SELECT * FROM TABLENAME WHERE column_name != value;

Syntax to update data from the table using the NOT EQUAL operator

UPDATE TABLENAME SET column_name = value WHERE column_name != value;

Syntax to delete data from the table using the NOT EQUAL operator

DELETE FROM TABLENAME WHERE column_name != value;

Let's understand the below example, which explains how to execute NOT Equal Operator in SQL query:

Consider the existing tables, which have the following records:

Table:Employees

Příklad 1: Write a query to display the employee records from the employees’ table whose employee salary is not equal to 55500.

SELECT * FROM EMPLOYEES WHERE SALARY != 55500;

From the above query, we are fetching the employee data from the employees' table where the employee salary is not equal to 55500.

Výstup:

As we can see in the output, only those records are displayed whose Salary is not equal to 55500.

Příklad 2: Write a query to display the employee records from the employees’ table whose employee city is not equal to Pune or department is not equal to FMW.

SELECT * FROM EMPLOYEES WHERE CITY != 'PUNE' AND DEPARTMENT != 'FMW';

From the above query, we are fetching the employee data from the employees’ table where employee city is not equal to Pune and Department is not equal to FMW.

Výstup:

As we can see in the output, only those records are displayed whose employee city is not equal to Pune and Department is not equal to FMW.

Příklad 3: Write a query to update the employee records from the employees’ table whose employee city is not equal to ‘Mumbai’ and department is not equal to 'Oracle’.

UPDATE EMPLOYEES SET SALARY = SALARY * 1.2 WHERE CITY != 'MUMBAI' AND DEPARTMENT != 'ORACLE';

From the above query, we are updating the employee records from the employees' table whose City is not equal to Mumbai and department is not equal to Oracle.

To cross-check whether the records are updated or not, we will run the SELECT statement.

SELECT * FROM EMPLOYEES WHERE CITY != 'MUMBAI' AND DEPARTMENT != 'ORACLE';

As we can see, the records are updated successfully, whose CityCity is not equal to Mumbai and the department is not equal to Oracle.

Příklad 4: Write a query to delete the employee records from the employees’ table whose employee city is not equal to ‘Pune’ and Manager Id is not equal to 2.

DELETE FROM EMPLOYEES WHERE CITY != 'PUNE' OR MANAGERID != 2;

From the above query, we are deleting the employee records from the employees’ table whose CityCity is not equal to 'Pune' or Manager id is not equal to 2.

To cross-check whether the record is deleted or not, we will run the SELECT statement.

SELECT * FROM EMPLOYEES;

As we can see, the employee records whose CityCity is not equal to Pune or manager id is not equal to 2 are deleted successfully.

SQL Less Than Operator

This operator query displays only those records from the table which are less than from the right side of the SQL query.

The Less Than comparison operator checks in the query if the left-side value is lesser than the right-side value. If the condition meets the satisfied criteria, this operator displays the right side values.

Syntax to access data from the table using the LESS THAN operator

SELECT * FROM TABLENAME WHERE column_name < value;

Syntax to update data from the table using the LESS THAN operator

UPDATE TABLENAME SET column_name = value WHERE column_name < value;

Syntax to delete data from the table using the LESS THAN operator

DELETE FROM TABLENAME WHERE column_name < value;

Let's understand the below example, which explains how to execute LESS THAN Operator in SQL query:

Consider the existing tables, which have the following records:

Table:Emp

Příklad 1: Write a query to display the employee records from the emp table whose employee salary is less than 55500.

SELECT * FROM EMP WHERE SALARY < 55500;

From the above query, we fetched the employees' record from the emp table where employee salary is less than 55500.

Výstup:

As we can see, only those records are displayed whose employee salary is less than 55500.

Příklad 2: Write a query to display the employee records from the emp table whose employee-manager id is less than 3.

SELECT * FROM EMP WHERE MANAGERId < 3;

From the above query, we are fetching the employees' records from the emp table where the employee-manager id is less than 3.

Výstup:

As we can see, only those records are displayed whose employee-manager id is less than 3.

SQL Less Than Equals to Operator

Less Than Equals to operator query displays only those data from the table which are less than and Equal to the right-side in the SQL query.

The Less Than Equal to comparison operator check in the query if the left-side value is lesser than an Equal to the right-side value. If the condition meets the satisfied criteria, this operator displays those lesser than and Equal to the right side values.

Syntax to access data from the table using the LESS THAN EQUALS to the operator

SELECT * FROM TABLENAME WHERE column_name <= value;

Syntax to update data from the table using the LESS THAN EQUALS to the operator

UPDATE TABLENAME SET column_name = value WHERE column_name <= value;

Syntax to delete data from the table using the LESS THAN EQUALS to the operator

DELETE FROM TABLENAME WHERE column_name <= value;

Let's understand the below example, which explains how to execute LESS THAN EQUALS to Operator in SQL query:

Consider the existing tables, which have the following records:

Table:Emp

Příklad 1: Write a query to display the employee records from the emp table whose employee salary is less than equals to 58000.

SELECT * FROM EMP WHERE SALARY <= 58000;

From the above query, we are fetching the employees' records from the emp table where employee salary is less than equal to 58000.

Výstup:

As we can see, only those records are displayed whose employee salary is less than equals to 58000.

Příklad 2: Write a query to display the employee records from the emp table whose employee-manager id is less than equal to 2.

SELECT * FROM EMP WHERE MANAGERId <= 2;

From the above query, we are fetching the employees' records from the emp table where the employee-manager id is less than equal to 2.

Výstup:

As we can see, only those records are displayed whose employee-manager id is less than equal to 2.

SQL Greater Than Operator

This operator query displays only those records from the table which are greater than from the right side of the SQL query.

The query's Greater Than comparison operator checks if the left-side value is greater than the right-side value. If the condition met the satisfied criteria, this operator displays those greater than the right-side values.

Syntax to access data from the table using the GREATER THAN operator

SELECT * FROM TABLENAME WHERE column_name > value;

Syntax to update data from the table using the GREATER THAN operator

UPDATE TABLENAME SET column_name = value WHERE column_name > value;

Syntax to delete data from the table using the GREATER THAN to operator

DELETE FROM TABLENAME WHERE column_name > value;

Let's understand the below example, which explains how to execute GREATER THAN Operator in SQL query:

Consider the existing tables, which have the following records:

Table:Emp

Příklad 1: Write a query to display the employee records from the emp table whose employee salary is greater than 60000.

SELECT * FROM EMP WHERE SALARY > 60000;

From the above query, we fetched the employees' records from the emp table where employee salary is greater than 60000.

Výstup:

As we can see, only those records are displayed whose employee salary is greater than 60000.

SQL Greater Than Equals to Operator

This operator query displays only those records from the table greater than and Equal to the right-side in the SQL query.

The query checks the Greater Than Equal to comparison operator if the left-side value is greater than and Equal to the right-side value. If the condition meets the criteria, this operator displays those values greater than and Equal to the right-side values.

Syntax to access data from the table using the GREATER THAN EQUALS TO operator

SELECT * FROM TABLENAME WHERE column_name >= value;

Syntax to update data from the table using the GREATER THAN EQUALS TO operator

UPDATE TABLENAME SET column_name = value WHERE column_name >= value;

Syntax to delete data from the table using the GREATER THAN EQUALS TO operator

DELETE FROM TABLENAME WHERE column_name >= value;

Příklad 1: Write a query to display the employee records from the emp table whose employee salary is greater than equals to 60000.

SELECT * FROM EMP WHERE SALARY >= 60000;

From the above query, we are fetching the employees’ record from the emp table where employee salary is greater than equals to 60000.

Výstup:

As we can see, only those records are displayed whose employee salary is greater than equals to 60000.