CREATE TABLE with PostgreSQL types - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this CREATE TABLE statement?

Consider the following SQL statement in PostgreSQL:

CREATE TABLE employees (
  id SERIAL PRIMARY KEY,
  name VARCHAR(50) NOT NULL,
  salary NUMERIC(10,2),
  hired_on DATE
);

What is the data type of the id column after table creation?

PostgreSQL

CREATE TABLE employees (
  id SERIAL PRIMARY KEY,
  name VARCHAR(50) NOT NULL,
  salary NUMERIC(10,2),
  hired_on DATE
);

A INTEGER with auto-increment behavior

B VARCHAR with length 50

C NUMERIC with precision 10 and scale 2

D DATE type

💡 Hint

Remember that SERIAL is a shorthand for an integer column that auto-increments.

In PostgreSQL, SERIAL is a pseudo-type that creates an integer column with auto-incrementing behavior using a sequence. So the 'id' column becomes an INTEGER with auto-increment.

❓ query_result

intermediate

What is the maximum length of the 'description' column?

Given this table creation:

CREATE TABLE products (
  product_id UUID PRIMARY KEY,
  description TEXT,
  price MONEY
);

What is the maximum length allowed for the description column?

PostgreSQL

CREATE TABLE products (
  product_id UUID PRIMARY KEY,
  description TEXT,
  price MONEY
);

A 1000 characters

B 255 characters

C 50 characters

D Unlimited length (only limited by system memory)

💡 Hint

TEXT type in PostgreSQL can store very large strings.

The TEXT data type in PostgreSQL can store strings of any length, limited only by the maximum size of a field in the database system.

📝 Syntax

advanced

Which CREATE TABLE statement is syntactically correct for a JSONB column?

Choose the correct PostgreSQL CREATE TABLE statement that defines a column named data with JSONB type:

A CREATE TABLE logs (id SERIAL PRIMARY KEY, data JSONB NOT NULL);

B CREATE TABLE logs (id SERIAL PRIMARY KEY, data JSON NOTB NULL);

C CREATE TABLE logs (id SERIAL PRIMARY KEY, data JSONB NULLABLE);

D CREATE TABLE logs (id SERIAL PRIMARY KEY, data JSONB NOTNULL);

💡 Hint

Check the spelling and syntax of the NOT NULL constraint.

Option A uses the correct JSONB type and the correct NOT NULL syntax. Other options have syntax errors or invalid keywords.

❓ optimization

advanced

Which data type is best for storing a US phone number in PostgreSQL?

You want to store US phone numbers in a PostgreSQL table. Which data type is the most appropriate for efficient storage and querying?

A VARCHAR(14) to store formatted phone numbers like '[phone]'

B BIGINT to store only digits without formatting

C TEXT to allow any phone number format

D CHAR(10) to store only digits without formatting

💡 Hint

Consider storage size and ability to perform numeric comparisons.

BIGINT stores numeric digits efficiently and allows numeric operations. VARCHAR or TEXT store strings but use more space and are slower for numeric queries.

🧠 Conceptual

expert

What happens if you define a column as SERIAL and also specify a default value?

In PostgreSQL, consider this table definition:

CREATE TABLE test (
  id SERIAL DEFAULT 1000 PRIMARY KEY
);

What will be the behavior of the id column when inserting rows without specifying id?

A The sequence starts at 1000 and increments from there

B An error occurs because SERIAL and DEFAULT cannot be combined

C The default value 1000 is used for all inserts, ignoring the sequence

D The sequence generated by SERIAL overrides the default 1000 value

💡 Hint

Think about how DEFAULT interacts with SERIAL's implicit sequence.

Specifying DEFAULT 1000 overrides the implicit sequence default created by SERIAL, so all inserts without id use 1000, causing duplicate key errors if multiple rows inserted.