下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。
DBX_MYSQL
(int)
DBX_ODBC
(int)
DBX_PGSQL
(int)
DBX_MSSQL
(int)
DBX_FBSQL
(int)
DBX_OCI8
(int)
DBX_SYBASECT
(int)
DBX_SQLITE
(int)
DBX_PERSISTENT
(int)
DBX_RESULT_INFO
(int)
DBX_RESULT_INDEX
(int)
DBX_RESULT_ASSOC
(int)
DBX_RESULT_UNBUFFERED
(int)
DBX_COLNAMES_UNCHANGED
(int)
DBX_COLNAMES_UPPERCASE
(int)
DBX_COLNAMES_LOWERCASE
(int)
DBX_CMP_NATIVE
(int)
DBX_CMP_TEXT
(int)
DBX_CMP_NUMBER
(int)
DBX_CMP_ASC
(int)
DBX_CMP_DESC
(int)