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Chapter 4 QUERYING AND MODIFYING DATA 225 Sometimes data is entered into a database with leading or trailing spaces. To retrieve data free of these spaces, use the trim functions: LTRIM and RTRIM. SELECT RTRIM (LTRIM( this is an example ))+ TESTER As example Concatenation processes are often performed to generate names from a fully normalized database, as shown in Figure 4.5. You can change the direction of text or make an expression uppercase or lowercase by using these three functions: REVERSE, UPPER, and LOWER. Look at the following example: SELECT UPPER( mustafa ), LOWER( MUNAWAR ), REVERSE( Mustafa ) Concatenation of a string value to a NULL string results in NULL. A check should be performed for string content in situations where concatenated information could be partially or completely NULL. The SUBSTRING Function It may be that you want to return a part of a string rather than the whole string. The SUBSTRING function, which returns a part of a character or binary string, can be used for this. The syntax for SUBSTRING is SUBSTRING (expression, start, length) FIGURE 4.5 Concatenation to formulate names from multiple columns.

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