Inserting and querying data in Supabase

Introduction

We insert data to save new information. We query data to find and use saved information.

You want to save a new user's details in your app.

You need to show a list of products from your database.

You want to update a dashboard with the latest sales data.

You want to find a specific record by its ID.

You want to check all entries made today.

Syntax

Supabase

const { data, error } = await supabase
  .from('table_name')
  .insert([{ column1: 'value1', column2: 'value2' }])

const { data, error } = await supabase
  .from('table_name')
  .select('*')
  .eq('column1', 'value1')

Use insert to add new rows to a table.

Use select to get rows. Use filters like eq to find specific rows.

Examples

Insert a new user named Alice who is 30 years old.

Supabase

await supabase
  .from('users')
  .insert([{ name: 'Alice', age: 30 }])

Get all users from the users table.

Supabase

await supabase
  .from('users')
  .select('*')

Get users whose name is Alice.

Supabase

await supabase
  .from('users')
  .select('*')
  .eq('name', 'Alice')

Sample Program

This program inserts a user named Bob, then queries all users named Bob and prints both results.

Supabase

import { createClient } from '@supabase/supabase-js'

const supabaseUrl = 'https://xyzcompany.supabase.co'
const supabaseKey = 'public-anonymous-key'
const supabase = createClient(supabaseUrl, supabaseKey)

async function run() {
  // Insert a new user
  const { data: insertData, error: insertError } = await supabase
    .from('users')
    .insert([{ name: 'Bob', age: 25 }])

  if (insertError) {
    console.error('Insert error:', insertError.message)
    return
  }

  console.log('Inserted data:', insertData)

  // Query users named Bob
  const { data: queryData, error: queryError } = await supabase
    .from('users')
    .select('*')
    .eq('name', 'Bob')

  if (queryError) {
    console.error('Query error:', queryError.message)
    return
  }

  console.log('Queried data:', queryData)
}

run()

Important Notes

Always check for errors after inserting or querying data.

Insert data as an array of objects, even if inserting one row.

Use filters like eq, lt, gt to narrow queries.

Summary

Insert data to add new rows to your database.

Query data to find and use saved information.

Check for errors to handle problems early.

Practice

1. What does the insert() method do in Supabase?

easy

A. Adds new rows of data to a table

B. Deletes rows from a table

C. Updates existing rows in a table

D. Retrieves data from a table

Solution

1. Step 1: Understand the purpose of insert()

   The insert() method is used to add new data entries (rows) into a database table.

2. Step 2: Differentiate from other methods

   Methods like delete() remove data, update() changes existing data, and select() retrieves data. Only insert() adds new rows.

3. Final Answer:

   Adds new rows of data to a table -> Option A

4. Quick Check:

   insert() = Add rows [OK]

Hint: Insert means add new data rows [OK]

Common Mistakes:

• Confusing insert() with update()
• Thinking insert() deletes data
• Mixing insert() with select()

2. Which of the following is the correct syntax to insert a new user with name 'Alice' into the 'users' table using Supabase client?

easy

A. supabase.insert('users').from({name: 'Alice'})

B. supabase.users.insert('Alice')

C. supabase.table('users').add({name: 'Alice'})

D. supabase.from('users').insert({name: 'Alice'})

Solution

1. Step 1: Recall Supabase insert syntax

   The correct syntax uses supabase.from('table').insert(data) to add data.

2. Step 2: Match syntax with options

   supabase.from('users').insert({name: 'Alice'}) matches the correct pattern: supabase.from('users').insert({name: 'Alice'}). Others misuse method order or names.

3. Final Answer:

   supabase.from('users').insert({name: 'Alice'}) -> Option D

4. Quick Check:

   from('table').insert(data) = correct syntax [OK]

Hint: Use from('table').insert({data}) to add rows [OK]

Common Mistakes:

• Swapping method order like insert().from()
• Using non-existent methods like add()
• Passing data as string instead of object

3. Given this code snippet, what will be the output?

const { data, error } = await supabase
  .from('products')
  .select('*')
  .eq('category', 'books');
console.log(data);

medium

A. An empty array always

B. An error message because of wrong syntax

C. An array of products where category is 'books'

D. All products regardless of category

Solution

1. Step 1: Understand the query filters

   The select('*') fetches all columns, and .eq('category', 'books') filters rows where category equals 'books'.

2. Step 2: Predict the output of console.log(data)

   It will print an array of product objects matching the category 'books'. If no error, data contains matching rows.

3. Final Answer:

   An array of products where category is 'books' -> Option C

4. Quick Check:

   select('*').eq() filters rows = filtered array [OK]

Hint: eq() filters rows by column value [OK]

Common Mistakes:

• Thinking select('*') returns all rows without filter
• Assuming syntax error due to chaining
• Expecting empty array without data

4. What is wrong with this Supabase insert code?

const { data, error } = await supabase
  .from('orders')
  .insert(['item', 'quantity']);

medium

A. insert() expects an array of objects, not an array of strings

B. from() should be called after insert()

C. insert() cannot be awaited

D. Missing .select() after insert()

Solution

1. Step 1: Check insert() argument type

   The insert() method requires an array of objects representing rows, e.g., [{item: 'apple', quantity: 2}]. Passing an array of strings is invalid.

2. Step 2: Verify method order and usage

   Calling from() before insert() is correct. Awaiting insert() is valid. .select() after insert() is optional for returning data.

3. Final Answer:

   insert() expects an array of objects, not an array of strings -> Option A

4. Quick Check:

   insert() needs array of objects [OK]

Hint: Insert data as objects inside array [OK]

Common Mistakes:

• Passing array of strings instead of objects
• Calling from() after insert()
• Thinking insert() can't be awaited

5. You want to insert multiple new users and then immediately fetch all users with age over 20. Which code correctly does this in Supabase?

hard

A. const { data } = await supabase.from('users').select('*').gt('age', 20);
await supabase.from('users').insert([{name: 'Bob', age: 25}, {name: 'Eve', age: 22}]);

B. await supabase.from('users').insert([{name: 'Bob', age: 25}, {name: 'Eve', age: 22}]);
const { data } = await supabase.from('users').select('*').gt('age', 20);

C. await supabase.from('users').insert({name: 'Bob', age: 25, name: 'Eve', age: 22});
const { data } = await supabase.from('users').select('*').gt('age', 20);

D. await supabase.from('users').insert([{name: 'Bob', age: 25}, {name: 'Eve', age: 22}]).select('*').gt('age', 20);

Solution

1. Step 1: Insert multiple users correctly

   Use insert() with an array of objects: [{name: 'Bob', age: 25}, {name: 'Eve', age: 22}]. A single malformed object is invalid.

2. Step 2: Query users with age > 20 after insertion

   Insert first, then use a separate query: supabase.from('users').select('*').gt('age', 20). Querying before insert misses new data; chaining select().gt() after insert() is invalid.

3. Final Answer:

   Insert first, then query with .gt('age', 20) -> Option B

4. Quick Check:

   Insert then query = correct order [OK]

Hint: Insert first, then query filtered data [OK]

Common Mistakes:

• Querying before inserting new data
• Passing single object instead of array for multiple inserts
• Chaining select() after insert() incorrectly