Informix Guide to SQL: Tutorial Composing SELECT Statements

This chapter introduced sample syntax and results for basic kinds of SELECT statements that are used to query a relational database. The section Single-Table SELECT Statements shows how to perform the following actions:

• Select columns and rows from a table with the SELECT and FROM clauses
• Select rows from a table with the SELECT, FROM, and WHERE clauses
• Use the DISTINCT or UNIQUE keyword in the SELECT clause to eliminate duplicate rows from query results
• Sort retrieved data with the ORDER BY clause and the DESC keyword
• Select and order data that contains non-English characters
• Use the BETWEEN, IN, MATCHES, and LIKE keywords and various relational operators in the WHERE clause to create a comparison condition
• Create comparison conditions that include values, exclude values, find a range of values (with keywords, relational operators, and subscripting), and find a subset of values
• Use exact-text comparisons, variable-length wildcards, and restricted and unrestricted wildcards to perform variable text searches
• Use the logical operators AND, OR, and NOT to connect search conditions or Boolean expressions in a WHERE clause
• Use the ESCAPE keyword to protect special characters in a query
• Search for null values with the IS NULL and IS NOT NULL keywords in the WHERE clause
• Use the FIRST clause to specify that a query returns only a specified number of the rows that match the conditions of the SELECT statement
• Use arithmetic operators in the SELECT clause to perform computations on number fields and display derived data
• Use substrings and subscripting to tailor your queries
• Assign display labels to computed columns as a formatting tool for reports

This chapter also introduced simple join conditions that enable you to select and display data from two or more tables. The section Multiple-Table SELECT Statements describes how to perform the following actions:

• Create a Cartesian product
• Include a WHERE clause with a valid join condition in your query to constrain a Cartesian product
• Define and create a natural join and an equi-join
• Join two or more tables on one or more columns
• Select rows from tables within a table hierarchy
• Use aliases as a shortcut in multiple-table queries
• Retrieve selected data into a separate, temporary table with the INTO TEMP clause to perform computations outside the database
• Select tables from a database other than the current database