"多步操作产生错误,请检查每一步的状态值" 导致原因和排查过程

原SQL写法：
 //生成表结构
// sErr := OpenSql('SELECT CAST(0 AS INTEGER) AS iStep, CAST('''' AS VARCHAR(40)) AS StepName, CAST('''' AS VARCHAR(2000)) AS MsgText', qryMsg);
 
改ORACLE数据库后：
错误写法：  sErr := OpenSql('SELECT 0 AS iStep,NULL AS StepName, NULL AS MsgText FROM DUAL', QryMsg);
正确写法：  sErr := OpenSql('SELECT CAST(0 AS INT) AS iStep,CAST('''' AS VARCHAR2(40)) AS StepName, 
CAST('''' AS VARCHAR2(2000)) AS MsgText FROM DUAL', QryMsg);
 
原因：这里并不是简单的查询赋空值，而是给QryMsg(TADOQuery)数据集定义数据结构和类型，包括字段类型，因为后面有循环添加数据操作：
 
QryMsg.AppendRecord([I, lstHint[J], TMemo(Obj).Lines.Text]);
QryMsg.AppendRecord([102, '校对', string(P^)]);
QryMsg.AppendRecord([101, '打字', string(P^)]);

 

总结：如出现此错误，并且有数据库写操作，请仔细检查数据库表结构类型、字段长度及写入的数据是否匹配。