我创建了一个在 MySQL Workbench 中正常工作的查询,但是当我在 Eclipse 中运行它时却无法正常工作。与数据库的连接工作正常,因为通过更简单的查询我得到了正确的结果。
java代码:
String queryAlter = "SELECT count(*) ";
queryAlter += "INTO @exist ";
queryAlter += "FROM information_schema.columns ";
queryAlter += "WHERE table_schema = database() ";
queryAlter += "and COLUMN_NAME = 'question" + (100 + number + 1)+"' ";
queryAlter += "AND table_name = '"+ tableName+"'; ";
queryAlter += "set @query = IF(@exist <= 0, 'alter table "+ tableName+" add column question" + (100 + number + 1)+" varchar(2048) NULL', ";
queryAlter += "'select \\'Column Exists\\' status'); ";
queryAlter += "use joomla30; ";
queryAlter += "prepare stmt from @query; ";
queryAlter += "EXECUTE stmt;";
我收到这条消息:
发生错误。也许用户名/密码无效 com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException:你的SQL语法有错误;查看与您的 MySQL 服务器版本对应的手册,了解在第 1 行的 'set @query = IF(@exist <= 0, 'alter table n0x3c_twoquestions_table add column qu' 附近使用的正确语法
查询的字符串也是:
SELECT count(*) INTO @exist FROM information_schema.columns WHERE table_schema = database() and COLUMN_NAME = 'question101' AND table_name = 'n0x3c_twoquestions_table'; set @query = IF(@exist <= 0, 'alter table n0x3c_twoquestions_table add column question101 varchar(2048) NULL', 'select \'Column Exists\' status'); use joomla30; prepare stmt from @query; EXECUTE stmt;
我也在我从MySQL Query works in PhpMyAdmin but not in JAVA Eclipse读到的java中尝试过这个:
String s1 = "SELECT count(*) INTO @exist FROM information_schema.columns WHERE table_schema = database() and COLUMN_NAME = 'question" + (100 + number + 1)+"' AND table_name = '"+ tableName+"'; ";
String s2 = "set @query = IF(@exist <= 0, 'alter table "+ tableName+" add column question" + (100 + number + 1)+" varchar(2048) NULL', 'select \\'Column Exists\\' status'); ";
String s3 = "use joomla30; ";
String s4 = "prepare stmt from @query; ";
stmt.addBatch(s1);
stmt.addBatch(s2);
stmt.addBatch(s3);
stmt.addBatch(s4);
stmt.executeBatch();
conn1.commit();
但是我有这个错误:
java.sql.BatchUpdateException:无法通过 executeUpdate() 发出 SELECT。
最佳答案
您可以使用两个不同的查询。
首先是检查列是否存在:
String countQuery = "select count(*) from information_schema.columns WHERE table_schema = database() and COLUMN_NAME = 'question106' and table_name='n0x3c_twoquestions_table'";
然后如果countQuery
返回0,就可以执行alterQuery
:
String alterQuery = "alter table n0x3c_twoquestions_table add column question106 varchar(2048) NULL";
如果你不想使用两个不同的查询,你可以通过异常捕获来处理:
String alterQuery = "alter table n0x3c_twoquestions_table add column question106 varchar(2048) NULL";
try (Connection conn = ds.getConnection(); PreparedStatement ps = conn.prepareStatement(alterQuery)) {
ps.execute();
} catch (SQLException e) {
if (e.getErrorCode() == 1060) {
columnExists = true;
} else {
// TODO handle exception
}
}
我找到了错误代码 MySQL Server error codes .
关于java - 查询在 MySql workbench 中运行,但不在 Java eclipse 中运行,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25160103/