What is nested case in SQL?

Nested CASE: CASE in IF ELSE

Table of Contents

First, IF Statement will execute and if Case Condition in SQL server is False then ELSE statement will execute. Else contain Nested CASE Statement in SQL inside it.

What is nested CASE statement?

In the Nested CASE expression, the outer statement executes until satisfying a condition. Once the condition is met, the inner CASE expression executes and returns a single result. If no condition is met in the outer statement, CASE expression returns the value in the ELSE statement.

How do you give multiple conditions in a case in SQL?

Here are 3 different ways to apply a case statement using SQL:

(1) For a single condition: CASE WHEN condition_1 THEN result_1 ELSE result_2 END AS new_field_name.
(2) For multiple conditions using AND: CASE WHEN condition_1 AND condition_2 THEN result_1 ELSE result_2 END AS new_field_name.

How do you optimize multiple cases in SQL?

SELECT contract_number, product_description, product, CASE WHEN ( x. produkt = ‘product_name’ AND ( SELECT COUNT(DISTINCT damagenumber) FROM table z WHERE date BETWEEN add_months(trunc(sysdate), – 6) AND sysdate AND internalname <> ‘CONDITION’ AND x. contract_number = z. contract_number GROUP BY z.

Can you have multiple conditions in a CASE statement?

Multiple conditions in CASE statement
You can evaluate multiple conditions in the CASE statement.

What is CASE statement in SQL?

The SQL CASE Expression
The CASE expression goes through conditions and returns a value when the first condition is met (like an if-then-else statement). So, once a condition is true, it will stop reading and return the result. If no conditions are true, it returns the value in the ELSE clause.

Can you have multiple conditions in a case statement?

Can CASE statement return multiple values?

@yzhang – With CASE only the first match will return values. If you want the possibility of multiple conditions mathcing each input row, you need to make each check indpendantly, and UNION the results together.

How can I make SQL query faster?

How To Speed Up SQL Queries

Use column names instead of SELECT *
Avoid Nested Queries & Views.
Use IN predicate while querying Indexed columns.
Do pre-staging.
Use temp tables.
Use CASE instead of UPDATE.
Avoid using GUID.
Avoid using OR in JOINS.

How can I improve my query performance?

It’s vital you optimize your queries for minimum impact on database performance.

Define business requirements first.
SELECT fields instead of using SELECT *
Avoid SELECT DISTINCT.
Create joins with INNER JOIN (not WHERE)
Use WHERE instead of HAVING to define filters.
Use wildcards at the end of a phrase only.

What are the two types of case expressions?

The CASE expression is a conditional expression, similar to if/then/else statements found in other languages. CASE is used to specify a result when there are multiple conditions. There are two types of CASE expressions: simple and searched.

Can case statement return multiple values?

Can you use a subquery in a Case Statement?

Subquery Example
The following query example uses the Subquery inside a Case Statement in SQL Server. First, the Subquery will execute and finds the Average of the Sales amount. Next, it will check whether the Sales are greater than the Average Sales (1970.9055).

Can you have multiple conditions in a Case Statement?

Why should nested SQL queries be avoided?

Personally I prefer to avoid nested queries until they are necessary for the simple reason that nested queries can make the code less human readable and make debugging and collaboration more painful.

Which is fastest database?

MySQL is the fastest SQL database. It is one of the fastest among relational databases.

Which join is faster in SQL?

INNER JOIN
As discussed in Point 1, usually INNER JOIN is more restrictive and returns fewer results and is therefore faster.

How do I optimize a large SQL query?

Supercharge Your SQL Queries for Production Databases

Define business requirements first.
SELECT fields instead of using SELECT *
Avoid SELECT DISTINCT.
Create joins with INNER JOIN (not WHERE)
Use WHERE instead of HAVING to define filters.
Use wildcards at the end of a phrase only.
Use LIMIT to sample query results.

What are the types of CASE expression?

Can you nest case statements in Oracle SQL?

Can CASE statements be nested? type_pre, As we see, Oracle allows nested CASE operators.

Can we write WHERE clause in case statement?

CASE can be used in any statement or clause that allows a valid expression. For example, you can use CASE in statements such as SELECT, UPDATE, DELETE and SET, and in clauses such as select_list, IN, WHERE, ORDER BY, and HAVING.

What is difference between subquery and nested query?

When a query is included inside another query, the Outer query is known as Main Query, and Inner query is known as Subquery. In Nested Query, Inner query runs first, and only once. Outer query is executed with result from Inner query.

Are nested queries bad practice?

The problem with nested queries is that in many circumstances they will perform just fine, but change the data slightly and they can seriously harm database performance in MySQL.

What are the 4 types of database?

Four types of database management systems
hierarchical database systems. network database systems. object-oriented database systems.

What DB does Google use?

In Google Cloud use Cloud SQL for any general-purpose SQL database and Cloud Spanner for large-scale globally scalable, strongly consistent use cases. In general, if your data structure may change later and if scale and availability is a bigger requirement then a non-relational database is a preferable choice.

What is nested case in SQL?