| Character functions are used mainly to compare, join, search, and extract a segment of a string or a value in a column. There are several character functions available to the SQL programmer. The following sections illustrate the application of ANSI concepts in some of the leading implementations of SQL, such as in Oracle, Sybase, SQLBase, Informix, and SQL Server.  | The ANSI concepts discussed in this book are just thatconcepts. Standards provided by ANSI are simply guidelines for how the use of SQL in a relational database should be implemented. With that thought, keep in mind that the specific functions discussed in this hour are not necessarily the exact functions that you may use in your particular implementation. Yes, the concepts are the same, and the way the functions work are generally the same, but function names and actual syntax may differ . |
Concatenation Concatenation, along with most other functions, is represented slightly differently among various implementations. The following examples show the use of concatenation in Oracle and SQL Server. | In Oracle | | SELECT 'JOHN' 'SON' returns JOHNSON | | In SQL Server | | SELECT 'JOHN' + 'SON' returns JOHNSON | | In MySQL | | SELECT CONCAT('JOHN' , 'SON') returns JOHNSON | The syntax for Oracle is  COLUMN_NAME [ '' ] COLUMN_NAME [ COLUMN_NAME ] The syntax for SQL Server is COLUMN_NAME + [ '' + ] COLUMN_NAME [ COLUMN_NAME ] The syntax for MySQL is CONCAT(COLUMN_NAME , [ '' , ] COLUMN_NAME [ COLUMN_NAME ] | Example | Meaning | | SELECT CITY + STATE FROM EMPLOYEE_TBL; | This SQL Server statement concatenates the values for city and state into one value. | | SELECT CITY ', ' STATE FROM EMPLOYEE_TBL; | This Oracle statement concatenates the values for city and state into one value, placing a comma between the values for city and state. | | SELECT CITY + '' + STATE FROM EMPLOYEE_TBL; | This SQL Server statement concatenates the values for city and state into one value, placing a space between the two original values. | Example:   SELECT LAST_NAME ', ' FIRST_NAME NAME FROM EMPLOYEE_TBL;  NAME ----------------- STEPHENS, TINA PLEW, LINDA GLASS, BRANDON GLASS, JACOB WALLACE, MARIAH SPURGEON, TIFFANY 6 rows selected. | | Notice the use of single quotation marks and a comma in the preceding SQL statement. Most characters and symbols are allowed if enclosed by single quotations marks. Some implementations may use double quotation marks for literal string values. |
TRANSLATE The TRANSLATE function searches a string of characters and checks for a specific character, makes note of the position found, searches the replacement string at the same position, and then replaces that character with the new value. The syntax is TRANSLATE(CHARACTER SET, VALUE1, VALUE2) | Example | Meaning | | SELECT TRANSLATE (CITY,'IND','ABC' FROM EMPLOYEE_TBL);B, and D with C. | This SQL statement substitutes every occurrence of I in the string with A, replaces all occurrences with C. | The following example illustrates the use of TRANSLATE with real data: SELECT CITY, TRANSLATE(CITY,'IND','ABC') FROM EMPLOYEE_TBL; CITY TRANSLATE(CI ------------ ------------ GREENWOOD GREEBWOOC INDIANAPOLIS ABCAABAPOLAS WHITELAND WHATELABC INDIANAPOLIS ABCAABAPOLAS INDIANAPOLIS ABCAABAPOLAS INDIANAPOLIS ABCAABAPOLAS 6 rows selected. Notice in this example that all occurrences of I were replaced with A, N with B, and D with C. In the city INDIANAPOLIS, IND was replaced with ABC, but in GREENWOOD, D was replaced with C. Also notice how the value WHITELAND was translated. REPLACE The REPLACE function is used to replace every occurrence of a character(s) with a specified character(s). The use of this function is similar to the TRANSLATE function; only one specific character or string is replaced within another string. The syntax is REPLACE('VALUE', 'VALUE', [ NULL ] 'VALUE') | Example | Meaning | | SELECT REPLACE(FIRST__'T', 'B') FROM EMPLOYEE_TBL | This statement returns all NAME, the first names and changes any occurrence of T to a B. | SELECT CITY, REPLACE(CITY,'I','Z') FROM EMPLOYEE_TBL; CITY REPLACE(CITY) ------------ ------------- GREENWOOD GREENWOOD INDIANAPOLIS ZNDZANAPOLZS WHITELAND WHZTELAND INDIANAPOLIS ZNDZANAPOLZS INDIANAPOLIS ZNDZANAPOLZS INDIANAPOLIS ZNDZANAPOLZS 6 rows selected. UPPER Most implementations have a way to control the case of data by using functions. The UPPER function is used to convert lowercase letters to uppercase letters for a specific string. The syntax is as follows : UPPER(character string) | Example | Meaning | | SELECT UPPER(LAST_NAME)FROM EMPLOYEE_TBL;LAST_NAME | This SQL statement converts all characters in the column to uppercase. | SELECT UPPER(CITY) FROM EMPLOYEE_TBL; UPPER(CITY) ------------- GREENWOOD INDIANAPOLIS WHITELAND INDIANAPOLIS INDIANAPOLIS INDIANAPOLIS 6 rows selected. LOWER The converse of the UPPER function, the LOWER function is used to convert uppercase letters to lowercase letters for a specific string. The syntax is as follows: LOWER(character string) | Example | Meaning | | SELECT LOWER(LAST_NAME)FROM EMPLOYEE_TBL;LAST_NAME | This SQL statement converts all characters in the column to lowercase. | SELECT LOWER(CITY) FROM EMPLOYEE_TBL; LOWER(CITY) ------------- greenwood indianapolis whiteland indianapolis indianapolis indianapolis 6 rows selected. SUBSTR Taking an expression's substring is common in most implementations of SQL, but the function name may differ, as shown in the following Oracle and SQL Server examples. The syntax for Oracle is SUBSTR(COLUMN NAME, STARTING POSITION, LENGTH) The syntax for SQL Server is SUBSTRING(COLUMN NAME, STARTING POSITION, LENGTH) The only difference between the two implementations is the spelling of the function name. | Example | Meaning | | SELECT SUBSTRING(EMP_ID,1,3) FROM EMPLOYEE_TBL | This SQL statement returns the first three characters of EMP_ID. | | SELECT SUBSTRING(EMP_ID,4,2) FROM EMPLOYEE_TBL | This SQL statement returns the fourth and fifth characters of EMP_ID. | | SELECT SUBSTRING(EMP_ID,6,4) FROM EMPLOYEE_TBL | This SQL statement returns the sixth through the ninth characters of EMP_ID. | The following is an example that is compatible with Microsoft SQL Server and MySQL: SELECT EMP_ID, SUBSTRING(EMP_ID,1,3) FROM EMPLOYEE_TBL; EMP_ID SUB --------- --- 311549902 311 442346889 442 213764555 213 313782439 313 220984332 220 443679012 443 6 rows affected. SELECT EMP_ID, SUBSTR(EMP_ID,1,3) FROM EMPLOYEE_TBL; EMP_ID SUB --------- --- 311549902 311 442346889 442 213764555 213 313782439 313 220984332 220 443679012 443 6 rows selected. | | Notice the difference between the feedback of the two queries. The first example returns the feedback 6 rows affected and the second returns 6 rows selected. You will see differences such as this between the various implementations. |
INSTR The INSTR function is a variation of the POSITION function; it is used to search a string of characters for a specific set of characters and report the position of those characters. The syntax is as follows: INSTR(COLUMN NAME, 'SET', [ START POSITION [ , OCCURRENCE ] ]); | Example | Meaning | | SELECT INSTR(STATE,'I',1,1) FROM EMPLOYEE_TBL; | This SQL statement returns the position of the first occurrence of the letter I for each state in EMPLOYEE_TBL. | SELECT PROD_DESC, INSTR(PROD_DESC,'A',1,1) FROM PRODUCTS_TBL; PROD_DESC INSTR(PROD_DESC,'A',1,1) ------------------------- -------------------------- WITCHES COSTUME 0 PLASTIC PUMPKIN 18 INCH 3 FALSE PARAFFIN TEETH 2 LIGHTED LANTERNS 10 ASSORTED COSTUMES 1 CANDY CORN 2 PUMPKIN CANDY 10 PLASTIC SPIDERS 3 ASSORTED MASKS 1 KEY CHAIN 7 OAK BOOKSHELF 2 11 rows selected. Notice that if the searched character A was not found in a string, the value 0 was returned for the position. LTRIM The LTRIM function is another way of clipping part of a string. This function and SUBSTRING are in the same family. LTRIM is used to trim characters from the left of a string. The syntax is LTRIM(CHARACTER STRING [ ,'set' ]) | Example | Meaning | | SELECT LTRIM(FIRST_NAME,'LES') FROM CUSTOMER_TBL WHERE FIRST_NAME ='LESLIE'; | This SQL statement trims the characters LES from the left of all names that are LESLIE. | SELECT POSITION, LTRIM(POSITION,'SALES') FROM EMPLOYEE_PAY_TBL; POSITION LTRIM(POSITION, --------------- --------------- MARKETING MARKETING TEAM LEADER TEAM LEADER SALES MANAGER MANAGER SALESMAN MAN SHIPPER HIPPER SHIPPER HIPPER 6 rows selected. The S in SHIPPER was trimmed off, even though SHIPPER does not contain the string SALES. The first four characters of SALES were ignored. The searched characters must appear in the same order of the search string and must be on the far left of the string. In other words, LTRIM will trim off all characters to the left of the last occurrence in the search string. RTRIM Like LTRIM, the RTRIM function is used to trim characters from the right of a string. The syntax is RTRIM(CHARACTER STRING [ ,'set' ]) | Example | Meaning | | SELECT RTRIM(FIRST_NAME, 'ON') FROM EMPLOYEE_TBL WHERE FIRST_NAME = 'BRANDON'; | This SQL statement returns the first name BRANDON and trims the ON, leaving BRAND as a result. | SELECT POSITION, RTRIM(POSITION,'ER') FROM EMPLOYEE_PAY_TBL; POSITION RTRIM(POSITION, --------------- --------------- MARKETING MARKETING TEAM LEADER TEAM LEAD SALES MANAGER SALES MANAG SALESMAN SALESMAN SHIPPER SHIPP SHIPPER SHIPP 6 rows selected. The string ER was trimmed from the right of all applicable strings. DECODE The DECODE function is not ANSIat least not at the time of this writingbut its use is shown here because of its great power. This function is used in SQLBase, Oracle, and possibly other implementations. DECODE is used to search a string for a value or string, and if the string is found, an alternative string is displayed as part of the query results. The syntax is DECODE(COLUMN NAME, 'SEARCH1', 'RETURN1',[ 'SEARCH2', 'RETURN2' ,'DEFAULT VALUE']) | Example | Meaning | | SELECT DECODE(LAST_NAME,'SMITH', 'JONES','OTHER') FROM EMPLOYEE_TBL; | This query searches the value of all last names in EMPLOYEE_TBL; if the value SMITH is found, JONES is displayed in its place.Any other names are displayed as OTHER, which is called the default value. | In the following example, DECODE is used on the values for CITY in EMPLOYEE_TBL: SELECT CITY, DECODE(CITY,'INDIANAPOLIS','INDY', 'GREENWOOD','GREEN', 'OTHER') FROM EMPLOYEE_TBL; CITY DECOD ------------ ----- GREENWOOD GREEN INDIANAPOLIS INDY WHITELAND OTHER INDIANAPOLIS INDY INDIANAPOLIS INDY INDIANAPOLIS INDY 6 rows selected. The output shows the value INDIANAPOLIS displayed as INDY, GREENWOOD displayed as GREEN, and all other cities displayed as OTHER. | 
