Expressions and operators

This document describes how to use boolean, numeric, and date expressions, as well as basic operators. In addition, it provides information on conditional expression and operators.

Basic operators

A large number of YSQL types have corresponding mathematical operators that are typically used for performing comparisons and mathematical operations. Operators allow you to specify conditions in YSQL statements and create links between conditions.

Mathematical operators

The following table lists some of the mathematical operators that you can use in YSQL.

The following examples show how to use mathematical operators in a SELECT statement:

SELECT 1+2;

SELECT 6/2;

SELECT ||/ 27.0;

Comparison operators

Comparison operators are binary. They return a boolean value true or false, depending on whether or not the comparison was asserted.

The following table lists comparison operators that you can use in YSQL.

Suppose you work with a database that includes the following table populated with data:

CREATE TABLE employees (
  employee_no integer PRIMARY KEY,
  name text,
  department text,
  salary integer
);

INSERT INTO employees (employee_no, name, department, salary)
  VALUES
  (1221, 'John Smith', 'Marketing', 50000),
  (1222, 'Bette Davis', 'Sales', 55000),
  (1223, 'Lucille Ball', 'Operations', 70000),
  (1224, 'John Zimmerman', 'Sales', 60000);

The following example shows a SELECT statement that returns employees whose employee numbers are greater than 1222:

SELECT * FROM employees WHERE employee_no > 1222;

The following is the output produced by the preceding example:

employee_no | name             | department   | salary
------------+------------------+--------------+--------------
1223        | Lucille Ball     | Operations   | 70000
1224        | John Zimmerman   | Sales        | 60000

String operators

The following table describes a string operator that you can use in YSQL.

Logical operators

The following table lists logical operators that you can use in YSQL.

The following example uses the sample table from Comparison operators and shows a SELECT statement that returns employees whose employee numbers are greater than or equal to 1222 and salary is greater than or equal to 70000:

SELECT * FROM employees WHERE employee_no >= 1222 AND SALARY >= 70000;

The following is the output produced by the preceding example:

employee_no | name             | department   | salary
------------+------------------+--------------+--------------
1223        | Lucille Ball     | Operations   | 70000

Bitwise operators

The following table lists bitwise operators that you can use in YSQL.

Bitwise operators can be applied to bit data types and data types related to it.

Basic expressions

An expression combines values, operators, and YSQL functions that evaluate to a value.

Typical YSQL expressions are similar to formulas. The following types of expressions are supported:

Boolean expressions

Boolean expressions retrieve data by matching a single value. The expression is included in the WHERE clause.

The following example uses the sample table from Comparison operators and shows a SELECT statement that returns employees whose salary is 60000:

SELECT * FROM employees WHERE salary = 60000;

The following is the output produced by the preceding example:

employee_no | name             | department   | salary
------------+------------------+--------------+--------------
1224        | John Zimmerman   | Sales        | 60000

Numeric expressions

The purpose of numeric expressions is to perform a mathematical operation on a query.

The following example shows how to use a basic numerical expression in a SELECT statement:

SELECT (10 + 5) AS ADDITION;

The following is the output produced by the preceding example:

addition
--------------
15

You can also use predefined functions such as avg(), sum(), or count() to perform aggregate data calculations on a table or a column.

The following example uses the sample table from Comparison operators and shows a SELECT statement that returns the number of employee rows:

SELECT count(*) AS "rows" FROM employees;

The following is the output produced by the preceding example:

rows
-----------
4

Date expressions

Date expressions retrieve the current system date and time, as shown in the following SELECT statement example:

SELECT CURRENT_TIMESTAMP;

The following is the output produced by the preceding example:

now
--------------
2021-03-15 14:38:28.078+05:30

You can use these expressions during data manipulation.

Conditional expressions and operators

Conditional expressions and operators assist you with forming conditional queries. YSQL supports CASE and CAST, among others.

CASE

The CASE expression enables you to add if-else logic to your queries (for example, to SELECT, WHERE, GROUP BY, and HAVING ).

The following is the syntax of the general form of the CASE expression:

CASE
  WHEN condition_a  THEN result_a
  WHEN condition_b  THEN result_b
  [WHEN ...]
  [ELSE result_else]
END

Each condition is a boolean expression. If it evaluates to false, CASE continues evaluation until it finds a condition that evaluates to true. If a condition evaluates to true, CASE returns the result that follows the condition and stops evaluation. If all conditions evaluate to false, CASE returns the result that follows ELSE. If ELSE is not included in the statement, the CASE expression returns NULL.

Suppose you work with a database that includes the following table populated with data:

CREATE TABLE employees (
  employee_no integer PRIMARY KEY,
  name text,
  department text
);

INSERT INTO employees VALUES
  (1221, 'John Smith', 'Marketing'),
  (1222, 'Bette Davis', 'Sales'),
  (1223, 'Lucille Ball', 'Operations'),
  (1224, 'John Zimmerman', 'Sales'),
  (1225, 'Lee Bo', 'Sales'),
  (1226, 'Frank Sinatra', 'Operations');

The following example uses the CASE expression in the SELECT statement to create labels for employees based on their employee number: if the number is smaller than 1223, the employee is a senior; if the number is greater than 1223 and smaller than or equal to 1225, the employee is intermediate; if the number is greater than 1225, the employee is a junior:

SELECT employee_no, name,
  CASE
    WHEN employee_no > 0
      AND employee_no <= 1223 THEN 'Senior'
    WHEN employee_no > 1223
      AND employee_no <= 1225 THEN 'Intermediate'
    WHEN employee_no > 1225 THEN 'Junior'
  END seniority
FROM employees
ORDER BY name;

The preceding example produces the following output, with a column alias seniority placed after the CASE expression:

 employee_no  | name           | seniority
--------------+----------------+--------------
1222          | Bette Davis    | Senior
1226          | Frank Sinatra  | Junior
1221          | John Smith     | Senior
1224          | John Zimmerman | Intermediate
1225          | Lee Bo         | Intermediate
1223          | Lucille Ball   | Senior

CAST

You can use the CAST operator to convert a value of one data type to another.

The following is the syntax of the CAST operator:

CAST (expression AS new_type);

expression is a constant, a table column, or an expression that evaluates to a value. new_type is a data type to which to convert the result of the expression.

The following example converts a string constant to an integer:

SELECT CAST ('25' AS INTEGER);

The following example converts a string constant to a date:

SELECT
  CAST ('2021-02-02' AS DATE),
  CAST ('02-DEC-2020' AS DATE);

The preceding example produces the following output:

 date       | date
------------+----------------
 2021-02-02 | 2020-12-02

YSQL supports another syntax for casting data types:

expression::type

The following example demonstrates the use of the :: operator:

SELECT
'25'::INTEGER,
'02-DEC-2020'::DATE;