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Chapter 8: Problem 4

Describe the six clauses in the syntax of an SQL query, and show what type of constructs can be specified in each of the six clauses. Which of the six clauses are required and which are optional?

Short Answer

Expert verified
The six clauses in SQL syntax are SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY. SELECT is used to select specific data and FROM specifies the table(s) to retrieve data from - both are required. WHERE is for filtering records, GROUP BY is for grouping identical values, HAVING filters result sets on a condition applying to aggregated values, and ORDER BY is for sorting the results - these four are optional.

Step by step solution

01

Clause 1: SELECT

The SELECT clause is used to select specific data from a database. It is the primary clause to select data from one or more tables. The SELECT clause essentially defines what data we are asking for. This clause is required.
02

Clause 2: FROM

The FROM clause specifies the table(s) from which the data needs to be retrieved. Data can be retrieved from a single table or multiple tables. This clause is required.
03

Clause 3: WHERE

The WHERE clause is used to filter records and its condition must be met for the records to be selected. It is optional.
04

Clause 4: GROUP BY

The GROUP BY clause group rows with identical values into aggregated data, like sum, average, or count. The GROUP BY clause is often used with aggregate functions like COUNT, SUM, AVG, MAX, or MIN to group the result set by one or more columns. This clause is optional.
05

Clause 5: HAVING

The HAVING clause lets you filter result sets on a condition that applies to aggregated values. HAVING is handy when you want to filter results after performing an aggregation. This clause is optional.
06

Clause 6: ORDER BY

The ORDER BY clause is used to sort the result-set by one or more columns. This clause is optional.

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Most popular questions from this chapter

Discuss how NULLs are treated in comparison operators in SQL. How are NULLs treated when aggregate functions are applied in an SQL query? How are NULLs treated if they exist in grouping attributes?

Describe conceptually how an SQL query will be executed by specifying the conceptual order of executing each of the six clauses.

List the data types that are allowed for SQL attributes.

How can the key and foreign key constraints be enforced by the DBMS? Is the enforcement technique you suggest difficult to implement? Can the constraint checks be executed efficiently when updates are applied to the database?

a. Design a relational database schema for your database application. b. Declare your relations, using the SQL DDL. c. Specify a number of queries in SQL that are needed by your database application. d. Based on your expected use of the database, choose some attributes that should have indexes specified on them. e. Implement your database, if you have a DBMS that supports SQL.
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