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 |
Note: With SQLite, the FormatOptions.StrsTrim works for all string data types.
参考： http://docwiki.embarcadero.com/RADStudio/XE6/en/Using_SQLite_with_FireDAC