BETWEEN for range filtering in PostgreSQL

Introduction

BETWEEN helps you find values that fall within a certain range, making it easy to filter data between two points.

Finding all sales made between two dates.

Selecting students with scores between 50 and 80.

Getting products priced between $10 and $50.

Filtering events happening between two times.

Syntax

PostgreSQL

SELECT column_name(s) FROM table_name WHERE column_name BETWEEN value1 AND value2;

BETWEEN includes both value1 and value2 in the results.

Works with numbers, dates, and text (alphabetical order).

Examples

Finds all orders placed in January 2023.

PostgreSQL

SELECT * FROM orders WHERE order_date BETWEEN '2023-01-01' AND '2023-01-31';

Selects students with scores from 60 to 80, inclusive.

PostgreSQL

SELECT name, score FROM students WHERE score BETWEEN 60 AND 80;

Lists products priced between $10 and $50.

PostgreSQL

SELECT product_name FROM products WHERE price BETWEEN 10 AND 50;

Sample Program

This creates a table of employees with salaries, then selects those earning between $60,000 and $80,000.

PostgreSQL

CREATE TABLE employees (id SERIAL PRIMARY KEY, name TEXT, salary INTEGER);
INSERT INTO employees (name, salary) VALUES
('Alice', 50000),
('Bob', 70000),
('Charlie', 60000),
('Diana', 80000);

SELECT name, salary FROM employees WHERE salary BETWEEN 60000 AND 80000 ORDER BY salary;

Important Notes

BETWEEN is inclusive: it includes the start and end values in the results.

For dates, use the format 'YYYY-MM-DD' or your database's date format.

You can use NOT BETWEEN to exclude a range.

Summary

BETWEEN filters data within a range including both ends.

It works with numbers, dates, and text.

Use it to simplify range queries instead of multiple conditions.

Practice

1. What does the BETWEEN operator do in PostgreSQL?

easy

A. Filters rows where a column's value is NULL.

B. Filters rows where a column's value is exactly equal to a single value.

C. Filters rows where a column's value is within a specified range, inclusive.

D. Filters rows where a column's value is outside a specified range.

Solution

1. Step 1: Understand the purpose of BETWEEN

   The BETWEEN operator checks if a value lies between two given values, including both ends.

2. Step 2: Compare with other filtering options

   Unlike equality or NULL checks, BETWEEN covers a range inclusively.

3. Final Answer:

   Filters rows where a column's value is within a specified range, inclusive. -> Option C

4. Quick Check:

   BETWEEN means inclusive range filter [OK]

Hint: BETWEEN includes both range ends, like a closed interval [OK]

Common Mistakes:

• Thinking BETWEEN excludes the range ends
• Confusing BETWEEN with equality (=)
• Assuming BETWEEN works only with numbers

2. Which of the following is the correct syntax to select rows where the column age is between 18 and 30 (inclusive)?

easy

A. SELECT * FROM users WHERE age BETWEEN 18 TO 30;

B. SELECT * FROM users WHERE age BETWEEN 18 AND 30;

C. SELECT * FROM users WHERE age >= 18 AND <= 30;

D. SELECT * FROM users WHERE age IN BETWEEN (18, 30);

Solution

1. Step 1: Recall correct BETWEEN syntax

   The correct syntax uses BETWEEN followed by the lower and upper bounds separated by AND.

2. Step 2: Check each option

   SELECT * FROM users WHERE age BETWEEN 18 AND 30; uses BETWEEN 18 AND 30 correctly; others have syntax errors or wrong keywords.

3. Final Answer:

   SELECT * FROM users WHERE age BETWEEN 18 AND 30; -> Option B

4. Quick Check:

   BETWEEN ... AND ... is correct syntax [OK]

Hint: BETWEEN always uses AND, not TO or commas [OK]

Common Mistakes:

• Using TO instead of AND
• Using incomplete comparison operators
• Misplacing parentheses or commas

3. Given the table orders with a column order_date of type DATE, what will this query return?

SELECT order_id FROM orders WHERE order_date BETWEEN '2023-01-01' AND '2023-01-31';

medium

A. Orders placed exactly on January 1, 2023, only.

B. All orders placed before January 1, 2023.

C. All orders placed after January 31, 2023.

D. All orders placed from January 1, 2023, to January 31, 2023, inclusive.

Solution

1. Step 1: Understand the BETWEEN date range

   The query filters orders where order_date is between '2023-01-01' and '2023-01-31', including both dates.

2. Step 2: Interpret the result set

   It returns all orders placed on any date from January 1 to January 31, 2023, inclusive.

3. Final Answer:

   All orders placed from January 1, 2023, to January 31, 2023, inclusive. -> Option D

4. Quick Check:

   BETWEEN includes both start and end dates [OK]

Hint: BETWEEN dates includes both start and end days [OK]

Common Mistakes:

• Assuming BETWEEN excludes the end date
• Confusing BETWEEN with less than or greater than only
• Thinking it returns only one date

4. Identify the error in this query:

SELECT * FROM products WHERE price BETWEEN 100, 500;

medium

A. The BETWEEN clause uses a comma instead of AND between values.

B. The price column cannot be used with BETWEEN.

C. BETWEEN requires parentheses around the values.

D. The query is correct and will run without errors.

Solution

1. Step 1: Check BETWEEN syntax

   BETWEEN requires two values separated by AND, not a comma.

2. Step 2: Identify the syntax error

   The query uses a comma between 100 and 500, which is invalid syntax.

3. Final Answer:

   The BETWEEN clause uses a comma instead of AND between values. -> Option A

4. Quick Check:

   BETWEEN needs AND, not commas [OK]

Hint: BETWEEN always uses AND, never commas [OK]

Common Mistakes:

• Using commas instead of AND
• Adding unnecessary parentheses
• Assuming BETWEEN works with any separator

5. You want to find all employees hired between January 1, 2020, and December 31, 2022, but exclude those hired exactly on January 1, 2020. Which query achieves this?

hard

A. All of the above queries will work correctly.

B. SELECT * FROM employees WHERE hire_date > '2020-01-01' AND hire_date <= '2022-12-31';

C. SELECT * FROM employees WHERE hire_date BETWEEN '2020-01-02' AND '2022-12-31';

D. SELECT * FROM employees WHERE hire_date BETWEEN '2020-01-01' AND '2022-12-31' AND hire_date <> '2020-01-01';

Solution

1. Step 1: Understand the requirement

   We want employees hired after January 1, 2020, up to December 31, 2022, excluding January 1, 2020 itself.

2. Step 2: Analyze each query

   SELECT * FROM employees WHERE hire_date BETWEEN '2020-01-01' AND '2022-12-31' AND hire_date <> '2020-01-01'; uses BETWEEN including '2020-01-01' but excludes it with <> condition.
   SELECT * FROM employees WHERE hire_date > '2020-01-01' AND hire_date <= '2022-12-31'; uses > and <= to exclude '2020-01-01' naturally.
   SELECT * FROM employees WHERE hire_date BETWEEN '2020-01-02' AND '2022-12-31'; shifts the BETWEEN range to start from '2020-01-02', excluding '2020-01-01'.

3. Step 3: Confirm all queries meet the condition

   All three queries exclude '2020-01-01' and include dates up to '2022-12-31'.

4. Final Answer:

   All of the above queries will work correctly. -> Option A

5. Quick Check:

   Multiple ways to exclude start date in range [OK]

Hint: Exclude start date by > or adjust BETWEEN start or add <> [OK]

Common Mistakes:

• Assuming BETWEEN excludes start date by default
• Using BETWEEN without excluding the start date
• Confusing BETWEEN with exclusive range