MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 21: ODBC API Reference

SQLForeignKeys

Conformance

Version Introduced: ODBC 1.0
Standards Compliance: ODBC

Summary

SQLForeignKeys can return:

• A list of foreign keys in the specified table (columns in the specified table that refer to primary keys in other tables).
  
  
• A list of foreign keys in other tables that refer to the primary key in the specified table.

The driver returns each list as a result set on the specified statement.

Syntax

SQLRETURN SQLForeignKeys(
     SQLHSTMT     StatementHandle,
     SQLCHAR *     PKCatalogName,
     SQLSMALLINT     NameLength1,
     SQLCHAR *     PKSchemaName,
     SQLSMALLINT     NameLength2,
     SQLCHAR *     PKTableName,
     SQLSMALLINT     NameLength3,
     SQLCHAR *     FKCatalogName,
     SQLSMALLINT     NameLength4,
     SQLCHAR *     FKSchemaName,
     SQLSMALLINT     NameLength5,
     SQLCHAR *     FKTableName,
     SQLSMALLINT     NameLength6);

Arguments

StatementHandle

[Input]
Statement handle.

PKCatalogName

[Input]
Primary key table catalog name. If a driver supports catalogs for some tables but not for others, such as when the driver retrieves data from different DBMSs, an empty string ("") denotes those tables that do not have catalogs. PKCatalogName cannot contain a string search pattern.

If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, PKCatalogName is treated as an identifier and its case is not significant. If it is SQL_FALSE, PKCatalogName is an ordinary argument; it is treated literally, and its case is significant. For more information, see "Arguments in Catalog Functions" in Chapter 7, "Catalog Functions."

NameLength1

[Input]
Length of *PKCatalogName, in bytes.

PKSchemaName

[Input]
Primary key table schema name. If a driver supports schemas for some tables but not for others, such as when the driver retrieves data from different DBMSs, an empty string ("") denotes those tables that do not have schemas. PKSchemaName cannot contain a string search pattern.

If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, PKSchemaName is treated as an identifier and its case is not significant. If it is SQL_FALSE, PKSchemaName is an ordinary argument; it is treated literally, and its case is significant.

NameLength2

[Input]
Length of *PKSchemaName, in bytes.

PKTableName

[Input]
Primary key table name. PKTableName cannot contain a string search pattern.

If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, PKTableName is treated as an identifier and its case is not significant. If it is SQL_FALSE, PKTableName is an ordinary argument; it is treated literally, and its case is significant.

NameLength3

[Input]
Length of *PKTableName.

FKCatalogName

[Input]
Foreign key table catalog name. If a driver supports catalogs for some tables but not for others, such as when the driver retrieves data from different DBMSs, an empty string ("") denotes those tables that do not have catalogs. FKCatalogName cannot contain a string search pattern.

If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, FKCatalogName is treated as an identifier and its case is not significant. If it is SQL_FALSE, FKCatalogName is an ordinary argument; it is treated literally, and its case is significant.

NameLength4

[Input]
Length of *FKCatalogName.

FKSchemaName

[Input]
Foreign key table schema name. If a driver supports schemas for some tables but not for others, such as when the driver retrieves data from different DBMSs, an empty string ("") denotes those tables that do not have schemas. FKSchemaName cannot contain a string search pattern.

If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, FKSchemaName is treated as an identifier and its case is not significant. If it is SQL_FALSE, FKSchemaName is an ordinary argument; it is treated literally, and its case is significant.

NameLength5

[Input]
Length of *FKSchemaName.

FKTableName

[Input]
Foreign key table name. FKTableName cannot contain a string search pattern.

If the SQL_ATTR_METADATA_ID statement attribute is set to SQL_TRUE, FKTableName is treated as an identifier and its case is not significant. If it is SQL_FALSE, FKTableName is an ordinary argument; it is treated literally, and its case is significant.

NameLength6

[Input]
Length of *FKTableName.

Returns

SQL_SUCCESS, SQL_SUCCESS_WITH_INFO, SQL_STILL_EXECUTING, SQL_ERROR, or SQL_INVALID_HANDLE.

Diagnostics

When SQLForeignKeys returns SQL_ERROR or SQL_SUCCESS_WITH_INFO, an associated SQLSTATE value may be obtained by calling SQLGetDiagRec with a HandleType of SQL_HANDLE_STMT and a Handle of StatementHandle. The following table lists the SQLSTATE values commonly returned by SQLForeignKeys and explains each one in the context of this function; the notation "(DM)" precedes the descriptions of SQLSTATEs returned by the Driver Manager. The return code associated with each SQLSTATE value is SQL_ERROR, unless noted otherwise.

Comments

For information about how the information returned by this function might be used, see "Uses of Catalog Data" in Chapter 7, "Catalog Functions."

If *PKTableName contains a table name, SQLForeignKeys returns a result set containing the primary key of the specified table and all of the foreign keys that refer to it. The list of foreign keys in other tables does not include foreign keys that point to unique constraints in the specified table.

If *FKTableName contains a table name, SQLForeignKeys returns a result set containing all of the foreign keys in the specified table that point to primary keys in others tables, and the primary keys in the other tables to which they refer. The list of foreign keys in the specified table does not contain foreign keys that refer to unique constraints in other tables.

If both *PKTableName and *FKTableName contain table names, SQLForeignKeys returns the foreign keys in the table specified in *FKTableName that refer to the primary key of the table specified in *PKTableName. This should be one key at most.

Note   For more information about the general use, arguments, and returned data of ODBC catalog functions, see Chapter 7, "Catalog Functions."

SQLForeignKeys returns results as a standard result set. If the foreign keys associated with a primary key are requested, the result set is ordered by FKTABLE_CAT, FKTABLE_SCHEM, FKTABLE_NAME, and KEY_SEQ. If the primary keys associated with a foreign key are requested, the result set is ordered by PKTABLE_CAT, PKTABLE_SCHEM, PKTABLE_NAME, and KEY_SEQ. The following table lists the columns in the result set.

The lengths of VARCHAR columns are not shown in the table; the actual lengths depend on the data source. To determine the actual lengths of the PKTABLE_CAT or FKTABLE_CAT, PKTABLE_SCHEM or FKTABLE_SCHEM, PKTABLE_NAME or FKTABLE_NAME, and PKCOLUMN_NAME or FKCOLUMN_NAME columns, an application can call SQLGetInfo with the SQL_MAX_CATALOG_NAME_LEN, SQL_MAX_SCHEMA_NAME_LEN, SQL_MAX_TABLE_NAME_LEN, and SQL_MAX_COLUMN_NAME_LEN options.

The following columns have been renamed for ODBC 3.x. The column name changes do not affect backward compatibility because applications bind by column number.

The following table lists the columns in the result set. Additional columns beyond column 14 (REMARKS) can be defined by the driver. An application should gain access to driver-specific columns by counting down from the end of the result set rather than specifying an explicit ordinal position. For more information, see "Data Returned by Catalog Functions" in Chapter 7, "Catalog Functions."

Code Example

As illustrated in the following table, this example uses three tables, named ORDERS, LINES, and CUSTOMERS.

In the ORDERS table, CUSTID identifies the customer to whom the sale has been made. It is a foreign key that refers to CUSTID in the CUSTOMERS table.

In the LINES table, ORDERID identifies the sales order with which the line item is associated. It is a foreign key that refers to ORDERID in the ORDERS table.

This example calls SQLPrimaryKeys to get the primary key of the ORDERS table. The result set will have one row; the significant columns are shown in the following table.

Next, the example calls SQLForeignKeys to get the foreign keys in other tables that reference the primary key of the ORDERS table. The result set will have one row; the significant columns are shown in the following table.

Finally, the example calls SQLForeignKeys to get the foreign keys in the ORDERS table that refer to the primary keys of other tables. The result set will have one row; the significant columns are shown in the following table.

#define TAB_LEN SQL_MAX_TABLE_NAME_LEN + 1
#define COL_LEN SQL_MAX_COLUMN_NAME_LEN + 1

LPSTR   szTable;              /* Table to display */

UCHAR szPkTable[TAB_LEN];   /* Primary key table name */
UCHAR szFkTable[TAB_LEN];   /* Foreign key table name */
UCHAR szPkCol[COL_LEN];     /* Primary key column */
UCHAR szFkCol[COL_LEN];     /* Foreign key column */

SQLHSTMT      hstmt;
SQLINTEGER    cbPkTable, cbPkCol, cbFkTable, cbFkCol, cbKeySeq;
SQLSMALLINT   iKeySeq;
SQLRETURN     retcode;

/* Bind the columns that describe the primary and foreign keys. */
/* Ignore the table schema, name, and catalog for this example. */

SQLBindCol(hstmt, 3, SQL_C_CHAR, szPkTable, TAB_LEN, &cbPkTable);
SQLBindCol(hstmt, 4, SQL_C_CHAR, szPkCol, COL_LEN, &cbPkCol);
SQLBindCol(hstmt, 5, SQL_C_SSHORT, &iKeySeq, TAB_LEN, &cbKeySeq);
SQLBindCol(hstmt, 7, SQL_C_CHAR, szFkTable, TAB_LEN, &cbFkTable);
SQLBindCol(hstmt, 8, SQL_C_CHAR, szFkCol, COL_LEN, &cbFkCol);

strcpy(szTable, "ORDERS");

/* Get the names of the columns in the primary key. */

retcode = SQLPrimaryKeys(hstmt,
         NULL, 0,             /* Catalog name */
         NULL, 0,             /* Schema name */
         szTable, SQL_NTS);   /* Table name */

while ((retcode == SQL_SUCCESS) || (retcode == SQL SUCCESS_WITH_INFO)) {

   /* Fetch and display the result set. This will be a list of the */
   /* columns in the primary key of the ORDERS table. */

   retcode = SQLFetch(hstmt);
   if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO)
      fprintf(out, "Table: %s Column: %s Key Seq: %hd \n", szPkTable, szPkCol,
      iKeySeq);
}

/* Close the cursor (the hstmt is still allocated). */

SQLFreeStmt(hstmt, SQL_CLOSE);

/* Get all the foreign keys that refer to ORDERS primary key.*/ 

retcode = SQLForeignKeys(hstmt,
         NULL, 0,            /* Primary catalog */
         NULL, 0,            /* Primary schema */
         szTable, SQL_NTS,   /* Primary table */
         NULL, 0,            /* Foreign catalog */
         NULL, 0,            /* Foreign schema */
         NULL, 0);           /* Foreign table */

while ((retcode == SQL_SUCCESS) || (retcode == SQL_SUCCESS_WITH_INFO)) {

/* Fetch and display the result set. This will be all of the */
/* foreign keys in other tables that refer to the ORDERS */
/* primary key. */

   retcode = SQLFetch(hstmt);
   if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO)
      fprintf(out, "%-s ( %-s ) <-- %-s ( %-s )\n", szPkTable,
               szPkCol, szFkTable, szFkCol);
}

/* Close the cursor (the hstmt is still allocated). */

SQLFreeStmt(hstmt, SQL_CLOSE);

/* Get all the foreign keys in the ORDERS table. */

retcode = SQLForeignKeys(hstmt,
         NULL, 0,             /* Primary catalog */
         NULL, 0,             /* Primary schema */
         NULL, 0,             /* Primary table */
         NULL, 0,             /* Foreign catalog */
         NULL, 0,             /* Foreign schema */
         szTable, SQL_NTS);   /* Foreign table */

while ((retcode == SQL_SUCCESS) || (retcode == SQL_SUCCESS_WITH_INFO)) {

/* Fetch and display the result set. This will be all of the */
/* primary keys in other tables that are referred to by foreign */
/* keys in the ORDERS table. */

   retcode = SQLFetch(hstmt);
   if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO)
      fprintf(out, "%-s ( %-s )--> %-s ( %-s )\n", szFkTable,
      szFkCol, szPkTable, szPkCol);
}

/* Free the hstmt. */

SQLFreeStmt(hstmt, SQL_DROP);

Related Functions