SELECT with Snowflake functions - Commands & Configuration

Introduction

When you want to get specific data from your Snowflake database, you use the SELECT statement. Snowflake functions help you change or calculate data as you get it, like changing text to uppercase or adding numbers.

When you want to see all customers whose names start with 'A'.

When you need to calculate the total price of items in an order.

When you want to change a date format to something easier to read.

When you want to count how many orders were placed last month.

When you want to combine first and last names into one full name.

Commands

This command selects the first names from the customers table and changes them to uppercase. It also calculates the length of the last names and only shows customers whose last names are longer than 5 characters.

Terminal

SELECT UPPER(first_name) AS upper_name, LENGTH(last_name) AS last_name_length FROM customers WHERE LENGTH(last_name) > 5;

Expected Output

UPPER_NAME   | LAST_NAME_LENGTH

JOHN         | 7

ALICE        | 6

This command combines first and last names into a full name for customers who signed up after January 1, 2023.

Terminal

SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM customers WHERE signup_date > '2023-01-01';

Expected Output

FULL_NAME

John Smith

Alice Johnson

This command selects order IDs and changes the order date into a simple year-month-day format for orders placed in 2024 or later.

Terminal

SELECT order_id, TO_VARCHAR(order_date, 'YYYY-MM-DD') AS formatted_date FROM orders WHERE order_date >= '2024-01-01';

Expected Output

ORDER_ID | FORMATTED_DATE

101      | 2024-02-15

102      | 2024-03-10

Key Concept

If you remember nothing else from this pattern, remember: Snowflake functions let you change or calculate data right when you select it, making your results more useful.

Common Mistakes

Using single quotes around column names instead of double quotes or no quotes.

Single quotes are for string values, not column names, so the query will fail.

Use double quotes for column names if needed or no quotes if the name is simple.

Forgetting to alias calculated columns with AS.

Without an alias, the output column name can be unclear or default to the function expression.

Always use AS to give a clear name to calculated columns.

Using functions on columns without considering NULL values.

Functions may return NULL or cause errors if the column has NULLs.

Use COALESCE or check for NULLs before applying functions.

Summary

Use SELECT with Snowflake functions to transform or calculate data as you retrieve it.

Alias your calculated columns with AS for clear output names.

Filter your data with WHERE to get only the rows you need.

Practice

1. What does the COUNT(*) function do in a Snowflake SELECT query?

easy

A. Calculates the sum of all numeric values in a column

B. Counts only rows with non-null values in a specific column

C. Counts all rows in the selected table or result set

D. Formats a date value into a string

Solution

1. Step 1: Understand COUNT(*) function

   The COUNT(*) counts every row regardless of nulls or values.

2. Step 2: Compare with other options

   Options B, C, and D describe different functions like COUNT(column), SUM(), and TO_CHAR().

3. Final Answer:

   Counts all rows in the selected table or result set -> Option C

4. Quick Check:

   COUNT(*) counts all rows [OK]

Hint: COUNT(*) counts every row, no matter what [OK]

Common Mistakes:

• Confusing COUNT(*) with COUNT(column)
• Thinking COUNT(*) ignores nulls
• Mixing COUNT with SUM or TO_CHAR

2. Which of the following is the correct syntax to convert a date column order_date to a string in format 'YYYY-MM-DD' using Snowflake?

easy

A. SELECT FORMAT_DATE(order_date, 'YYYY-MM-DD') FROM orders;

B. SELECT TO_CHAR(order_date, 'YYYY-MM-DD') FROM orders;

C. SELECT TO_STRING(order_date, 'YYYY-MM-DD') FROM orders;

D. SELECT CAST(order_date AS STRING, 'YYYY-MM-DD') FROM orders;

Solution

1. Step 1: Identify the correct function for date to string

   Snowflake uses TO_CHAR() to format dates as strings.

2. Step 2: Check syntax correctness

   SELECT TO_CHAR(order_date, 'YYYY-MM-DD') FROM orders; uses TO_CHAR(order_date, 'YYYY-MM-DD'), which is correct syntax. Others use invalid or non-existent functions.

3. Final Answer:

   SELECT TO_CHAR(order_date, 'YYYY-MM-DD') FROM orders; -> Option B

4. Quick Check:

   TO_CHAR formats dates to strings [OK]

Hint: Use TO_CHAR to format dates as strings [OK]

Common Mistakes:

• Using TO_STRING instead of TO_CHAR
• Trying FORMAT_DATE which doesn't exist in Snowflake
• Incorrect CAST syntax for formatting

3. Given the table sales with column amount, what is the result of this query?

SELECT SUM(amount) FROM sales WHERE amount > 100;

medium

A. Sum of amounts greater than 100

B. Average of amounts greater than 100

C. Count of rows where amount is greater than 100

D. Sum of all amounts including those less or equal to 100

Solution

1. Step 1: Understand the WHERE clause effect

   The WHERE clause filters rows to only those with amount > 100.

2. Step 2: Understand SUM function

   SUM adds all values of amount from the filtered rows.

3. Final Answer:

   Sum of amounts greater than 100 -> Option A

4. Quick Check:

   SUM with WHERE filters sums filtered rows [OK]

Hint: WHERE filters rows before SUM calculation [OK]

Common Mistakes:

• Including amounts less or equal to 100
• Confusing SUM with COUNT or AVG
• Ignoring WHERE clause effect

4. What is wrong with this Snowflake query?

SELECT TO_CHAR(order_date, YYYY-MM-DD) FROM orders;

medium

A. The date format string is not enclosed in quotes

B. TO_CHAR cannot be used on dates

C. Missing FROM clause

D. TO_CHAR requires three arguments

Solution

1. Step 1: Check TO_CHAR syntax

   The format string must be enclosed in single quotes, like 'YYYY-MM-DD'.

2. Step 2: Identify the error in the query

   The query uses YYYY-MM-DD without quotes, causing a syntax error.

3. Final Answer:

   The date format string is not enclosed in quotes -> Option A

4. Quick Check:

   Format strings need quotes in TO_CHAR [OK]

Hint: Always quote format strings in TO_CHAR [OK]

Common Mistakes:

• Forgetting quotes around format strings
• Thinking TO_CHAR needs more arguments
• Ignoring syntax errors from missing quotes

5. You want to find the average order amount rounded to 2 decimal places from the orders table. Which query correctly achieves this in Snowflake?

hard

A. SELECT AVG(ROUND(order_amount, 2)) FROM orders;

B. SELECT AVG(CAST(order_amount AS NUMBER(10,2))) FROM orders;

C. SELECT TO_CHAR(AVG(order_amount), '0.00') FROM orders;

D. SELECT ROUND(AVG(order_amount), 2) FROM orders;

Solution

1. Step 1: Understand rounding average correctly

   Rounding the average after calculating it gives the correct average rounded to 2 decimals.

2. Step 2: Analyze each option

   SELECT ROUND(AVG(order_amount), 2) FROM orders; rounds the AVG result, which is correct. SELECT AVG(ROUND(order_amount, 2)) FROM orders; rounds each value before averaging, which changes the result. SELECT TO_CHAR(AVG(order_amount), '0.00') FROM orders; converts to string, not numeric. SELECT AVG(CAST(order_amount AS NUMBER(10,2))) FROM orders; casts each value before averaging, which changes the result.

3. Final Answer:

   SELECT ROUND(AVG(order_amount), 2) FROM orders; -> Option D

4. Quick Check:

   Round after AVG for correct decimal rounding [OK]

Hint: Round the average, not individual values [OK]

Common Mistakes:

• Rounding before averaging changes results
• Using TO_CHAR instead of numeric rounding
• Casting individuals before averaging changes results