Update Commands

SQL Basics

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SQL Basics

Introduction

Basic Syntax

Basic Select Statements

Table Variables & Set Operators

Subqueries in the Where Clause

Subqueries in the From & Select Clause

The 'Join' Family Operators

Aggregation

Data Modification Statements

Insert Commands

Delete Commands

Update Commands

Let's find all users who do not currently have a ratingDate assigned to one of their rating's, and let's assign it a value.
Our query will look like this:
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SELECT *
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FROM User
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WHERE uID in (SELECT uID FROM Review WHERE ISNULL ratingDate);
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The query is going to look in the User relation and for each individual user, it will check for their uID in the Review table, and if the ratingDate returns true for ISNULL, then it will return that user in the end result.
If we ran the query, our results would include the users "Darrel Sherman", and "Chris Anderson", with a uID of 207 and 202 respectively.
Well now we want to update the ratingDate for these two individuals in the Review table. We would have to edit our query a little bit and have it look like this:
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UPDATE Review
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SET ratingDate = '2014'
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WHERE uID in (SELECT uID FROM Review WHERE ISNULL ratingDate) and ISNULL ratingDate;
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We added the UPDATE statement, and we're telling SQL to UPDATE the Review table. Find all the users with a uID that satisfy the subquery in the WHERE clause, but only consider reviews that currently have no ratingDate. Then take the ratingDate for those reviews and give it a value of '2014'. We'll assume we don't know the exact date that they rated the movie, but we know it was in 2014.

Delete Commands

Last modified 2yr ago

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