Various Common Character Functions
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.
Note
The ANSI concepts discussed in this book are just that—concepts. 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 |
The syntax for Oracle is
COLUMN_NAME || [ '' || ] COLUMN_NAME [ COLUMN_NAME ]
The syntax for SQL Server is
COLUMN_NAME + [ '' + ] COLUMN_sNAME [ 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.
Note
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); | This SQL statement substitutes every occurrence of I in the string with A, replaces all occurrences of N with B, and D 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_ NAME 'T', 'B') FROM EMPLOYEE_TBL | This statement returns all 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
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.
SUBSTR(COLUMN NAME, STARTING POSITION, LENGTH)
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 using Microsoft SQL Server:
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.
The following is an example using Oracle8:
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.
Note
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 see differences such as this between 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 FIRST_NAME = 'LESLIE'; | This SQL statement trims the characters LES from the left of all names that are WHERE 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 the 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 ANSI—at least not at the time of this writing—but 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 alternate string is displayed as part of the query results.
The syntax is
DECODE(COLUMN NAME, 'SEARCH1', 'RETURN1',[ 'SEARCH2', 'RETURN2' ,'DEFAULT åVALUE'])
| 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 thevalue 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.