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. . . exec sql delete from salesreps where quota < 150000; if (strcmp(sqlca.sqlstate,"00000")) goto error_routine; . . . error_routine: printf("SQL error: %s\n",sqlca.sqlstate); exit(); . . .
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Figure 17-12.
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A C program excerpt with SQLSTATE error checking
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The WHENEVER Statement
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It quickly becomes tedious for a programmer to write programs that explicitly check the SQLCODE value after each embedded SQL statement. To simplify error handling, embedded SQL supports the WHENEVER statement, shown in Figure 17-15. The WHENEVER statement is a directive to the SQL precompiler, not an executable statement. It tells the precompiler to automatically generate error-handling code following every executable embedded SQL statement and specifies what the generated code should do. You can use the WHENEVER statement to tell the precompiler how to handle three different exception conditions: I WHENEVER SQLERROR tells the precompiler to generate code to handle errors (negative SQLCODEs). I WHENEVER SQLWARNING tells the precompiler to generate code to handle warnings (positive SQLCODEs). I WHENEVER NOT FOUND tells the precompiler to generate code that handles a particular warning the warning generated by the DBMS when your program tries to retrieve query results when no more are remaining. This use of the WHENEVER statement is specific to the singleton SELECT and the FETCH statements, and is described in the section Single-Row Queries.
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To retrieve statement-level information and determine how many diagnostic errors:
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GET DIAGNOSTICS
hostvar
NUMBER MORE COMMAND_FUNCTION DYNAMIC_FUNCTION ROW_COUNT
To retrieve information about an individual diagnostic error:
GET DIAGNOSTICS EXCEPTION err_number
hostvar
CONDITION_NUMBER RETURNED_SQLSTATE CLASS_ORIGIN SUBCLASS_ORIGIN SERVER_NAME CONNECTION_NAME CONSTRAINT_CATALOG CONSTRAINT_SCHEMA CONSTRAINT_NAME CATALOG_NAME SCHEMA_NAME TABLE_NAME COLUMN_NAME CURSOR_NAME MESSAGE_TEXT MESSAGE_LENGTH MESSAGE_OCTET_LENGTH
PROGRAMMING
Figure 17-13.
The GET DIAGNOSTICS statement syntax diagram
Note that the SQL2 standard does not specify the SQLWARNING form of the WHENEVER statement, but most commercial SQL products support it.
SQL: The Complete Reference
. . . /* execute the DELETE statement & check for errors */ exec sql delete from salesreps where quota < 150000; if (strcmp(sqlca.sqlstate,"00000")) goto error_routine; /* DELETE successful; check how many rows deleted */ exec sql get diagnostics :numrows = ROW_COUNT; printf("%ld rows deleted\n",numrows); . . . error_routine: /* Determine how many errors reported */ exec sql get diagnostics :count = NUMBER; for (i=1; i<count; i++) { exec sql get diagnostics EXCEPTION :I :err = RETURNED_SQLSTATE, :msg = MESSAGE_TEXT; printf("SQL error # %d: code: %s message: %s\n", i, err, msg); } exit(); . . .
Figure 17-14.
A C program excerpt with GET DIAGNOSTICS error checking
For any of these three conditions, you can tell the precompiler to generate code that takes one of two actions: I WHENEVER/GOTO tells the precompiler to generate a branch to the specified label, which must be a statement label or statement number in the program. I WHENEVER/CONTINUE tells the precompiler to let the program s flow of control proceed to the next host language statement.
17:
Embedded SQL
Figure 17-15.
The WHENEVER statement syntax diagram
The WHENEVER statement is a directive to the precompiler, and its effect can be superseded by another WHENEVER statement appearing later in the program text. Figure 17-16 shows a program excerpt with three WHENEVER statements and four executable SQL statements. In this program, an error in either of the two DELETE statements results in a branch to error1 because of the first WHENEVER statement. An error in the embedded UPDATE statement flows directly into the following statements of the program. An error in the embedded INSERT statement results in a branch to error2. As this example shows, the main use of the WHENEVER/CONTINUE form of the statement is to cancel the effect of a previous WHENEVER statement. The WHENEVER statement makes embedded SQL error handling much simpler, and it is more common for an application program to use it than to check SQLCODE or SQLSTATE directly. Remember, however, that after a WHENEVER/GOTO statement appears, the precompiler will generate a test and a branch to the specified label for every embedded SQL statement that follows it. You must arrange your program so that the specified label is a valid target for branching from these embedded SQL statements, or use another WHENEVER statement to specify a different destination or cancel the effects of the WHENEVER/GOTO.
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