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
(integer)
DBX_ODBC
(integer)
DBX_PGSQL
(integer)
DBX_MSSQL
(integer)
DBX_FBSQL
(integer)
DBX_OCI8
(integer)
DBX_SYBASECT
(integer)
DBX_SQLITE
(integer)
DBX_PERSISTENT
(integer)
DBX_RESULT_INFO
(integer)
DBX_RESULT_INDEX
(integer)
DBX_RESULT_ASSOC
(integer)
DBX_RESULT_UNBUFFERED
(integer)
DBX_COLNAMES_UNCHANGED
(integer)
DBX_COLNAMES_UPPERCASE
(integer)
DBX_COLNAMES_LOWERCASE
(integer)
DBX_CMP_NATIVE
(integer)
DBX_CMP_TEXT
(integer)
DBX_CMP_NUMBER
(integer)
DBX_CMP_ASC
(integer)
DBX_CMP_DESC
(integer)