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This section describes C API data types other than those used for prepared statements. For information about the latter, see Section 25.2.5, “C API Prepared Statement Data typesâ€.
This structure represents a handle to one database connection. It is used for almost all MySQL functions. You should not try to make a copy of a
MYSQLstructure. There is no guarantee that such a copy will be usable.This structure represents the result of a query that returns rows (
SELECT,SHOW,DESCRIBE,EXPLAIN). The information returned from a query is called the result set in the remainder of this section.This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling
mysql_fetch_row().This structure contains information about a field, such as the field's name, type, and size. Its members are described in more detail here. You may obtain the
MYSQL_FIELDstructures for each field by callingmysql_fetch_field()repeatedly. Field values are not part of this structure; they are contained in aMYSQL_ROWstructure.This is a type-safe representation of an offset into a MySQL field list. (Used by
mysql_field_seek().) Offsets are field numbers within a row, beginning at zero.The type used for the number of rows and for
mysql_affected_rows(),mysql_num_rows(), andmysql_insert_id(). This type provides a range of0to1.84e19.On some systems, attempting to print a value of type
my_ulonglongdoes not work. To print such a value, convert it tounsigned longand use a%luprint format. Example:printf ("Number of rows: %lu\n", (unsigned long) mysql_num_rows(result));A boolean type, for values that are true (non-zero) or false (zero).
The MYSQL_FIELD structure contains the members
listed here:
char * nameThe name of the field, as a null-terminated string. If the field was given an alias with an
ASclause, the value ofnameis the alias.char * org_nameThe name of the field, as a null-terminated string. Aliases are ignored.
char * tableThe name of the table containing this field, if it isn't a calculated field. For calculated fields, the
tablevalue is an empty string. If the column is selected from a view,tablenames the view. If the table or view was given an alias with anASclause, the value oftableis the alias. For aUNION, the value is the empty string.char * org_tableThe name of the table, as a null-terminated string. Aliases are ignored. If the column is selected from a view,
org_tablenames the underlying table. For aUNION, the value is the empty string.char * dbThe name of the database that the field comes from, as a null-terminated string. If the field is a calculated field,
dbis an empty string. For aUNION, the value is the empty string.char * catalogThe catalog name. This value is always
"def".char * defThe default value of this field, as a null-terminated string. This is set only if you use
mysql_list_fields().unsigned long lengthThe width of the field. This corresponds to the display length, in bytes.
unsigned long max_lengthThe maximum width of the field for the result set (the length in bytes of the longest field value for the rows actually in the result set). If you use
mysql_store_result()ormysql_list_fields(), this contains the maximum length for the field. If you usemysql_use_result(), the value of this variable is zero.The value of
max_lengthis the length of the string representation of the values in the result set. For example, if you retrieve aFLOATcolumn and the “widest†value is-12.345,max_lengthis 7 (the length of'-12.345').If you are using prepared statements,
max_lengthis not set by default because for the binary protocol the lengths of the values depend on the types of the values in the result set. (See Section 25.2.5, “C API Prepared Statement Data typesâ€.) If you want themax_lengthvalues anyway, enable theSTMT_ATTR_UPDATE_MAX_LENGTHoption withmysql_stmt_attr_set()and the lengths will be set when you callmysql_stmt_store_result(). (See Section 25.2.7.3, “mysql_stmt_attr_set()â€, and Section 25.2.7.27, “mysql_stmt_store_result()â€.)unsigned int name_lengthThe length of
name.unsigned int org_name_lengthThe length of
org_name.unsigned int table_lengthThe length of
table.unsigned int org_table_lengthThe length of
org_table.unsigned int db_lengthThe length of
db.unsigned int catalog_lengthThe length of
catalog.unsigned int def_lengthThe length of
def.unsigned int flagsDifferent bit-flags for the field. The
flagsvalue may have zero or more of the following bits set:Flag Value Flag Description NOT_NULL_FLAGField can't be NULLPRI_KEY_FLAGField is part of a primary key UNIQUE_KEY_FLAGField is part of a unique key MULTIPLE_KEY_FLAGField is part of a non-unique key UNSIGNED_FLAGField has the UNSIGNEDattributeZEROFILL_FLAGField has the ZEROFILLattributeBINARY_FLAGField has the BINARYattributeAUTO_INCREMENT_FLAGField has the AUTO_INCREMENTattributeENUM_FLAGField is an ENUM(deprecated)SET_FLAGField is a SET(deprecated)BLOB_FLAGField is a BLOBorTEXT(deprecated)TIMESTAMP_FLAGField is a TIMESTAMP(deprecated)NUM_FLAGField is numeric; see additional notes following table NO_DEFAULT_VALUE_FLAGField has no default value; see additional notes following table Use of the
BLOB_FLAG,ENUM_FLAG,SET_FLAG, andTIMESTAMP_FLAGflags is deprecated because they indicate the type of a field rather than an attribute of its type. It is preferable to testfield->typeagainstMYSQL_TYPE_BLOB,MYSQL_TYPE_ENUM,MYSQL_TYPE_SET, orMYSQL_TYPE_TIMESTAMPinstead.NUM_FLAGindicates that a column is numeric. This includes columns with a type ofMYSQL_TYPE_DECIMAL,MYSQL_TYPE_TINY,MYSQL_TYPE_SHORT,MYSQL_TYPE_LONG,MYSQL_TYPE_FLOAT,MYSQL_TYPE_DOUBLE,MYSQL_TYPE_NULL,MYSQL_TYPE_TIMESTAMP,MYSQL_TYPE_LONGLONG,MYSQL_TYPE_INT24, andMYSQL_TYPE_YEAR.NO_DEFAULT_VALUE_FLAGindicates that a column has noDEFAULTclause in its definition. This does not apply toNULLcolumns (because such columns have a default ofNULL), or toAUTO_INCREMENTcolumns (which have an implied default value).NO_DEFAULT_VALUE_FLAGwas added in MySQL 5.0.2.The following example illustrates a typical use of the
flagsvalue:if (field->flags & NOT_NULL_FLAG) printf("Field can't be null\n");You may use the following convenience macros to determine the boolean status of the
flagsvalue:Flag Status Description IS_NOT_NULL(flags)True if this field is defined as NOT NULLIS_PRI_KEY(flags)True if this field is a primary key IS_BLOB(flags)True if this field is a BLOBorTEXT(deprecated; testfield->typeinstead)unsigned int decimalsThe number of decimals for numeric fields.
unsigned int charsetnrAn ID number that indicates the character set/collation pair for the field.
To distinguish between binary and non-binary data for string data types, check whether the
charsetnrvalue is 63. If so, the character set isbinary, which indicates binary rather than non-binary data. This enables you to distinguishBINARYfromCHAR,VARBINARYfromVARCHAR, and theBLOBtypes from theTEXTtypes.charsetnrvalues are the same as those displayed in theIdcolumn of theSHOW COLLATIONstatement or theIDcolumn of theINFORMATION_SCHEMACOLLATIONStable. You can use those information sources to see which character set and collation specificcharsetnrvalues indicate:mysql>
SHOW COLLATION WHERE Id = 63;+-----------+---------+----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +-----------+---------+----+---------+----------+---------+ | binary | binary | 63 | Yes | Yes | 1 | +-----------+---------+----+---------+----------+---------+ mysql>SELECT COLLATION_NAME, CHARACTER_SET_NAME->FROM INFORMATION_SCHEMA.COLLATIONS WHERE ID = 33;+-----------------+--------------------+ | COLLATION_NAME | CHARACTER_SET_NAME | +-----------------+--------------------+ | utf8_general_ci | utf8 | +-----------------+--------------------+enum enum_field_types typeThe type of the field. The
typevalue may be one of theMYSQL_TYPE_symbols shown in the following table.Type Value Type Description MYSQL_TYPE_TINYTINYINTfieldMYSQL_TYPE_SHORTSMALLINTfieldMYSQL_TYPE_LONGINTEGERfieldMYSQL_TYPE_INT24MEDIUMINTfieldMYSQL_TYPE_LONGLONGBIGINTfieldMYSQL_TYPE_DECIMALDECIMALorNUMERICfieldMYSQL_TYPE_NEWDECIMALPrecision math DECIMALorNUMERICfield (MySQL 5.0.3 and up)MYSQL_TYPE_FLOATFLOATfieldMYSQL_TYPE_DOUBLEDOUBLEorREALfieldMYSQL_TYPE_BITBITfield (MySQL 5.0.3 and up)MYSQL_TYPE_TIMESTAMPTIMESTAMPfieldMYSQL_TYPE_DATEDATEfieldMYSQL_TYPE_TIMETIMEfieldMYSQL_TYPE_DATETIMEDATETIMEfieldMYSQL_TYPE_YEARYEARfieldMYSQL_TYPE_STRINGCHARorBINARYfieldMYSQL_TYPE_VAR_STRINGVARCHARorVARBINARYfieldMYSQL_TYPE_BLOBBLOBorTEXTfield (usemax_lengthto determine the maximum length)MYSQL_TYPE_SETSETfieldMYSQL_TYPE_ENUMENUMfieldMYSQL_TYPE_GEOMETRYSpatial field MYSQL_TYPE_NULLNULL-type fieldYou can use the
IS_NUM()macro to test whether a field has a numeric type. Pass thetypevalue toIS_NUM()and it evaluates to TRUE if the field is numeric:if (IS_NUM(field->type)) printf("Field is numeric\n");
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User Comments
From above:
On some systems, attempting to print a value of type my_ulonglong does not work. To print such a value, convert it to unsigned long and use a %lu print format. Example:
printf ("Number of rows: %lu\n",
(unsigned long) mysql_num_rows(result));
This is naive in that this will ONLY work if the underlying unsigned long long is only as big as an unsigned long! This is only half of the total range of the ull.
A better way is to break it into 2 unsigned longs by shifting the upper 32-bits into a different unsigned long and then printf() both the upper and lower parts as unsigned longs each.
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