我有一个包含许多表的数据库，其中三个如下：
Controllers_Readers
-------------------
ControllerID: Number (Long Integer), Default 0, Indexed (Y, no Duplicated)
ReaderID: Number (Long Integer), Default 0, Indexed (Y, No Duplicates)
Controllers
-----------
ControllerID: Number (Long Integer), Default 0, Indexed (Y, No Duplicates)
Description: Short Text (32)
Name: Short Text (32)
...
Readers
-------
ReaderID: Number (Long Integer), Default 0, Indexed (Y, No Duplicates)
Direction: Number (Long Integer)
Description: Short Text (32)
Name: Short Text (32)
...
我有以下Java代码来检查表是否存在以及它是否包含特定列，基于this answer to a question about table metadata：
/* Use the metadata to check if a table exists and has a specific column */
public static boolean tableHasColumn(Connection con, String tableName, String colName)
throws ClassNotFoundException, SQLException, InstantiationException,
IllegalAccessException
{
boolean exists = false, hasCol = false;
ResultSet rs = null, r = null;
Statement s = null;
try {
DatabaseMetaData dbm = con.getMetaData();
rs = dbm.getTables(null, null, tableName, null);
if (rs.next() && rs.getRow() > -1) {
exists = true;
s = con.createStatement();
r = s.executeQuery("SELECT * FROM " + tableName + " LIMIT 1");
if (r.next()) {
ResultSetMetaData rsmd = r.getMetaData();
for (int col = 1; col < rsmd.getColumnCount(); col++) {
String name = rsmd.getColumnName(col);
logger.debug("Found column \"" + name + "\" in \"" + tableName + "\".");
if (name.equals(colName)) {
hasCol = true;
break;
}
}
}
}
} finally {
if (null != rs) {
try {
rs.close();
} catch (SQLException ex) {
logger.warn(
"Failed to close Resultset to DB while checking if table exists!"
);
}
}
}
logger.debug(
"Table (" + tableName + ") Exists: " + String.valueOf(exists).toUpperCase()
+ "\tHas Column (" + colName + "): " + String.valueOf(hasCol).toUpperCase()
);
return (exists && hasCol);
}
分别为"Controllers_Readers"和"ControllerID"提供tableName和colName的值，得到true的返回值。但是，当我运行以下查询时，我收到org.hsqldb.HsqlException: user lacks privilege or object not found: CONTROLLERS_READERS.CONTROLLERID
的错误消息：
SELECT C.Description AS cName, C.ControllerID AS CID,
D.DirectionText as dName, D.Direction AS dirNum, R.Description AS rName,
R.ReaderID AS RID, AP.Name AS aName, AP.Description as aDescrip, AP.PointID
FROM Controllers AS C, Controllers_Readers AS CR, Readers AS R,
Directions AS D, AccessPoints AS AP, Points_Controllers as PC
WHERE Controllers_Readers.ControllerID = Controllers.ControllerID
AND Readers.ReaderID = Controllers_Readers.ReaderID
AND Directions.Direction = Readers.Direction AND
Points_Controllers.ControllerID = Controllers.ControllerID
AND AccessPoints.PointID = Points_Controllers.PointID
GROUP BY Controllers.Description, Controllers.ControllerID,
Directions.DirectionText, Directions.Direction, Readers.Name,
Readers.Description, Readers.ReaderID, AccessPoints.Name,
AccessPoints.Description, AccessPoints.PointID
ORDER BY Controllers.Description, Controllers.ControllerID,
Directions.DirectionText, Directions.Direction, Readers.Name,
Readers.Description, Readers.ReaderID, AccessPoints.Name,
AccessPoints.Description, AccessPoints.PointID
相关日志输出如下：
2018-08-30 14:24:35 [DEBUG] db.Locations:35 - Location: LOCAL DB Path: \\sentinel.domain\TempStorage\Me\dbs\Redacted.mdb
2018-08-30 14:24:35 [DEBUG] db.Digger:767 - Connect to DB on path: \\sentinel.domain\TempStorage\Me\dbs\Redacted.mdb
2018-08-30 14:24:35 [INFO ] db.Digger:790 - Connecting to jdbc:ucanaccess:////sentinel.domain/TempStorage/Me/dbs//Redacted.mdb;openExclusive=false;concatNulls=false;ignoreCase=true
2018-08-30 14:24:37 [DEBUG] impl.DatabaseImpl:887 - Finished reading system catalog. Tables: [AccessNumbers, AccessNumbers_Controllers, AccessNumbers_Groups, AccessNumbers_Readers, AccessPoints, Areas, Areas_Controllers, Areas_Points, Areas_Timezones, Controllers, Controllers_Expanders, Controllers_Readers, Directions, Events, Expanders_Readers, Groups, Groups_Areas, Groups_Controllers, Groups_Timezones, Holidays, Points_Controllers, Points_Readers, Points_Timezones, ReaderExpanders, Readers, SelectedAreas, SelectedDates, Sites, Sites_Areas, Status, Storage, Timezones, Transactions, UserInformation, Users] (Db=Redacted.mdb)
2018-08-30 14:25:10 [DEBUG] db.Digger:884 - Found column "ControllerID" in "Controllers_Readers".
2018-08-30 14:25:10 [DEBUG] db.Digger:901 - Table (Controllers_Readers) Exists: TRUE Has Column: TRUE
2018-08-30 14:25:10 [ERROR] db.Digger:1180 - [UcanaccessSQLException]: UCAExc:::4.0.2 user lacks privilege or object not found: CONTROLLERS_READERS.CONTROLLERID
net.ucanaccess.jdbc.UcanaccessSQLException: UCAExc:::4.0.2 user lacks privilege or object not found: CONTROLLERS_READERS.CONTROLLERID
at net.ucanaccess.jdbc.UcanaccessStatement.executeQuery(UcanaccessStatement.java:210)
at db.Digger.loadAllControllerReaders(Digger.java:947)
at db.Digger.main(Digger.java:1177)
Caused by: java.sql.SQLSyntaxErrorException: user lacks privilege or object not found: CONTROLLERS_READERS.CONTROLLERID
at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source)
at org.hsqldb.jdbc.JDBCStatement.fetchResult(Unknown Source)
at org.hsqldb.jdbc.JDBCStatement.executeQuery(Unknown Source)
at net.ucanaccess.jdbc.UcanaccessStatement.executeQuery(UcanaccessStatement.java:208)
... 2 more
Caused by: org.hsqldb.HsqlException: user lacks privilege or object not found: CONTROLLERS_READERS.CONTROLLERID
at org.hsqldb.error.Error.error(Unknown Source)
at org.hsqldb.error.Error.error(Unknown Source)
at org.hsqldb.ExpressionColumn.checkColumnsResolved(Unknown Source)
at org.hsqldb.QueryExpression.resolve(Unknown Source)
at org.hsqldb.ParserDQL.compileCursorSpecification(Unknown Source)
at org.hsqldb.ParserCommand.compilePart(Unknown Source)
at org.hsqldb.ParserCommand.compileStatements(Unknown Source)
at org.hsqldb.Session.executeDirectStatement(Unknown Source)
at org.hsqldb.Session.execute(Unknown Source)
注意：db.Digger和db.Locations是我的应用程序中的类。 loadAllControllerReaders是执行SQL查询的方法。
通过MS Access（Office 365）对数据库运行相同的查询为我提供了一个包含列中值的结果集。为什么uCanAccess / HSQLDB无法做同样的事情（未能在ControllerID中找到Controllers_Readers列）？如何识别该列存在于表中？
我能够在HSQLDB本身（版本2.4.1）下重新创建您的问题。您在FROM子句中为表名设置了别名
... FROM Controllers AS C, Controllers_Readers AS CR, ...
但是您的WHERE子句使用无别名表名而不是别名
... WHERE Controllers_Readers.ControllerID = Controllers.ControllerID ...
所以实际的表名不被识别。这可以通过确认
Statement st = conn.createStatement();
st.execute("CREATE TABLE MY_TABLE (ID INT PRIMARY KEY, DT DATETIME)");
st.execute("INSERT INTO MY_TABLE (ID, DT) VALUES (1, '2018-12-23 00:11:22')");
ResultSet rs = st.executeQuery("SELECT X.DT FROM MY_TABLE AS X WHERE MY_TABLE.ID=1");
这也产生
java.sql.SQLSyntaxErrorException: user lacks privilege or object not found: MY_TABLE.ID
...
Caused by: org.hsqldb.HsqlException: user lacks privilege or object not found: MY_TABLE.ID
您还需要在剩余的子句（WHERE，GROUP BY，ORDER BY）中使用适当的别名。