FireDac 与数据库连接时字符集及对应的字段类型问题

近日在一个过程调用时发生一个奇怪现象， 异常返回意思是说， 数据的长度是【6】， 而字段定义的长度是【3】。 分析后认为： 调用过程你不涉及到对返回数据集的字段手动定义问题， 出现这个问题应是两边的字符集出了问题。

数据库字符集为 SIMPLIFIED CHINESE_CHINA.ZHS16GBK， 即双字节， 有可能FdConnection 的字符集设置出现匹配问题。 最后修改方案为：

1、修改 FDConnection 的 CharacterSet := 'UTF8' ， 即以 UTF8 与数据库连接，兼容所有类型数据库
2、修改在调用过程时所有原 ftString 改为 ftWideString

问题解决

找到一份针对 SQLLite 的字段对应关系，我想其他类型数据库也同理：

Type name	Description
ROWID | _ROWID_ | OID	dtInt64, Attrs = [caSearchable, caAllowNull, caROWID]
BIT | BOOL | BOOLEAN | LOGICAL | YESNO	dtBoolean
TINYINT | SHORTINT | INT8 [UNSIGNED]	dtSByte / dtByte
BYTE | UINT8	dtByte
SMALLINT | INT16 [UNSIGNED]	dtInt16 / dtUInt16
WORD | UINT16 | YEAR	dtUInt16
MEDIUMINT | INTEGER | INT | INT32 [UNSIGNED]	dtInt32 / dtUInt32
LONGWORD | UINT32	dtUInt32
BIGINT | INT64 | COUNTER | AUTOINCREMENT | IDENTITY [UNSIGNED]	dtInt64 / dtUInt64
LONGLONGWORD | UINT64	dtUInt64
REAL | FLOAT | DOUBLE	dtDouble
SINGLE [PRECISION] [(P, S)]	dtSingle / dtBCD / dtFmtBCD
DECIMAL | DEC | NUMERIC | NUMBER [UNSIGNED] [(P, S)]	dtSByte / dtInt16 / dtInt32 / dtInt64 dtByte / dtUInt16 / dtUInt32 / dtUInt64 dtBCD / dtFmtBCD
MONEY | SMALLMONEY | CURRENCY | FINANCIAL [(P, S)]	dtCurrency
DATE | SMALLDATE	dtDate
DATETIME | SMALLDATETIME	dtDateTime
TIMESTAMP	dtDateTimeStamp
TIME	dtTime
CHAR | CHARACTER [(L)]	dtAnsiString, Len = L, Attrs = [caFixedLen]
VARCHAR | VARCHAR2 | TYNITEXT | CHARACTER VARYING | CHAR VARYING [(L)]	dtAnsiString, Len = L
NCHAR | NATIONAL CHAR | NATIONAL CHARACTER [(L)]	dtWideString, Len = L, Attrs = [caFixedLen]
NVARCHAR | NVARCHAR2 | NATIONAL CHAR VARYING | STRING [(L)]	dtWideString, Len = L
RAW | TYNIBLOB | VARBINARY | BINARY | BINARY VARYING [(L)]	dtByteString, Len = L
BLOB | MEDIUMBLOB | IMAGE | LONGBLOB | LONG BINARY | LONG RAW | LONGVARBINARY | GENERAL | OLEOBJECT | TINYBLOB	dtBlob
MEDIUMTEXT | LONGTEXT | CLOB | MEMO | NOTE | LONG | LONG TEXT | LONGCHAR | LONGVARCHAR | TINYTEXT	dtMemo
TEXT | NTEXT | WTEXT | NCLOB | NMEMO | LONG NTEXT | LONG WTEXT | NATIONAL TEXT | LONGWCHAR | LONGWVARCHAR | HTML	dtWideMemo
XMLDATA | XMLTYPE | XML	dtXML
GUID | UNIQUEIDENTIFIER	dtGUID
Other data types	dtWideString

参考： http://docwiki.embarcadero.com/RADStudio/XE6/en/Using_SQLite_with_FireDAC