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"ORA-01858: a non-numeric character was found where a numeric was expected" when writing a query in a java class

I have a web application where 3 inputs are taken from the user and after clicking search button results are displayed. The three inputs are; id (not unique), startdate and enddate. I want to be able to get the results in these situations: If the user enters
only id
only start date (enrolldate in db table)
only end date (graduationdate in db table)
id and start date
when all the fields entered together
In my StudentManager.java class I have a SQL string like below;
final String SQL_STU = " select "
+ " t.name,"
+ " t.surname, "
+ " t.lecture,"
+ " from studenttable t "
+ " where t.school = 'CHC' "
+ " and t.id = case when '" + studentInfo.getID() + "'" +" is null then t.id else '" + studentInfo.getID() + "' end "
+ " and t.enrolldate >= case when '" + studentInfo.getStartDate() + "' is null then t.enrolldate else to_date('"
+ studentInfo.getStartDate() + "', 'DD.MM.YYYY HH24:MI:SS') end "
+ " and t.graduationdate >= case when '" + studentInfo.getEndDate() + "' is null then t.graduationdate else to_date('"
+ studentInfo.getEndDate() + "', 'DD.MM.YYYY HH24:MI:SS') end " ;
I will execute this query and get the results into a result set.
I have a couple of problems with this code; for example when I comment out this part:
+ " and t.enrolldate >= case when '" + studentInfo.getStartDate() + "' is null then t.enrolldate else to_date('"
+ studentInfo.getStartDate() + "', 'DD.MM.YYYY HH24:MI:SS') end "
+ " and t.graduationdate >= case when '" + studentInfo.getEndDate() + "' is null then t.graduationdate else to_date('"
+ studentInfo.getEndDate() + "', 'DD.MM.YYYY HH24:MI:SS') end " ;
It works without errors but when I give all the inputs null (id, date1, date2) it displays nothing. Shouldn't it display all the results since there is no specific id? (User will not be able to submit 3 empty fields but I am curious why it does not work like the way I mentioned? )
The other thing is when I execute the whole code (with to_date parts) it gives the error in the title. But it does not give any error when I execute like this:
final String SQL_STU = " select "
+ " t.name,"
+ " t.surname, "
+ " t.lecture,"
+ " from studenttable t "
+ " where t.school = 'CHC' "
+ " and t.enrolldate >= case when '" + studentInfo.getStartDate() + "' is null then t.enrolldate else to_date('"
+ studentInfo.getStartDate() + "', 'DD.MM.YYYY HH24:MI:SS') end " ;
So in summary I couldn't write the query the way I wanted. I am not that experienced with queries. If you know any better way you can also suggest it since I have come to a dead end. I also tried something with NVL but I could not make it work also.
Notes:
ID, StartDate,EndDate are type string in my StudentInfo.java class
id is type varchar and dates are type date in database table.(PL/SQL)

The best answer to your question is to use a prepared statement:
String sql = "SELECT t.name, t.surname, t.lecture ";
sql += "FROM studenttable t ";
sql += "WHERE t.school = 'CHC' AND "
sql += "t.id = COALESCE(?, t.id) AND ";
sql += "t.entrolldate >= COALESCE(?, t.enrolldate) AND ";
sql += "t.graduationdate >= COALESCE(?, t.graduationdate)";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setInt(1, studentInfo.getID());
ps.setDate(2, studentInfo.getStartDate());
ps.setDate(3, studentInfo.getEndDate());
ResultSet rs = ps.executeQuery();
while (rs.next()) {
// process a row
}
The reason why using a statement is preferred is that it frees you from having to manually marshal your Java date (and other type) variables into your Oracle SQL statement. Instead, the above code lets the JDBC driver worry about how to convert a Java date variable to the correct format in the actual SQL code. Also, statements allow you to write a SQL query with minimal concatenations, which reduces the chances for error and typos.
Note that you might have to call a setter other than PreparedStatement#setDate depending on the what getStartDate() and getEndDate() methods actually return in your Java code.

Sqlite Android Optimization

I have an application that works well. But I suspect that I can improve it if I optimize queries to the database. And I need suggestions.
This is part of my "select query":
private static final String SELECT = "SELECT " +
"dz.first_id AS first_id, " +
"dz._id AS _id, " +
"dz.att1 AS att1, " +
"dz.att2 AS att2, " +
"dz.att3 AS att3, " +
"dz.att4 AS att4, " +
"dz.att5 AS att5, " +
"d.var1 AS var1, " +
"d.name AS name, " +
"d.last_update AS last_update, " +
"d.image_url AS image_url, " +
"d.image_highlighted_url AS image_highlighted_url, " +
"d.var2 AS var2, " +
"d.type AS type, " +
"d.state AS state, " +
"d.sync AS sync, " +
"d.var3 AS var3 " +
"FROM table1 dz INNER JOIN table2 d " +
"ON d._id = dz.first_id ";
Cursor result = conn.rawQuery(SELECT, null);
*table1 and table2 have simple creation: only one _id integer PRIMARY KEY AUTOINCREMENT NOT NULL
It is useful to use views? Any other suggestion?
Thanks.

This query looks as cut and dry and they can get, I think your options are really either to see if you can somehow leave some unnecessary columns out of your select or alternatively to see that both dz.first_id and d._id have indexes setup. Perhaps add a index to dz with the following
CREATE INDEX index1 ON table1 (first_id);

How to put a real values in SQL query using postgreSQL?

I have some problems with an application developed in Java that uses postgreSQL as a DB. I managed to make a dummy query as follows:
String sql = "INSERT INTO voicemessages (UNIQUEID,MSGNM,DIR,CONTEXT,MACROCONTEXT,CALLERID, ORIGTIME,DURATION, FLAG,MAILBOXUSER,MAILBOXCONTEXT,RECORDING, LABEL, read ) "
+ "VALUES (1, 1, 'dir/dir1/msgs', 'message', 'message', '6001', '15/01/2015 13:31:25', '1:32', 'flag', 'Georgi Georgiev', 'Georgi Georgiev', '12314124', 'some label', false);";
And it works perfect when I execute the statement. A row in the DB is created and I am able to display the data using:
SELECT * FROM voicemessages;
The problem is when I create my own VoiceMail class and when I create an object from this type and put in the query the getters and setters for this object I receive some kind of an error:
org.postgresql.util.PSQLException: ERROR: column "dir" does not exist Hint:There is a column named "dir" in table "voicemessages", but it cannot be referenced from this part of the query.Position: 169
I am trying to insert a row by using and executing this:
String sql = "INSERT INTO voicemessages (UNIQUEID,MSGNM,DIR,CONTEXT,MACROCONTEXT,CALLERID, ORIGTIME,DURATION, FLAG,MAILBOXUSER,MAILBOXCONTEXT,RECORDING, LABEL, read ) "
+ "VALUES (" + message01.getUniqueId() + ", " + message01.getMessageNumber() + ", " + message01.getDirectory() + ", " + message01.getContext() + ", " + message01.getMacroContext() + ", " + message01.getCallerId() + ", " +message01.getOrigTime() + ", " + message01.getDuration() + ", " + message01.getFlag() + ", " + message01.getMailboxUser() + ", " +message01.getMailboxContext() + ", " + message01.getRecording() + ", " + message01.getLabel() + ", " + message01.getRead()+ ");"+" ";
Any help or suggestion is appreciated.
Thank you in advance!

Do not use Direct values use parameters for safety, What happens is that the SQL statement you pass is parsed to prepare and compiled by the database. So by sending the actual SQL separately from the parameters, you limit the risk of SQL injection

Mysql Insert query in Java

Im getting an sql syntax error somewhere at the end of this code line, i have tweaked it and mixed a bit with it but so far i haven't solved it.
strSQL="INSERT INTO " + tableName + " VALUES " + "(" + id + ",'" + rname + "','" + rfn + "','" + rmn + ")";
Any help appreciated!

You are missing a quote at the end
+ rmn + " )";
^---------here
But actually you should rather use Prepared Statements.

You have missed several ' signs. (not only in the end, but before and after the id)
strSQL="INSERT INTO " + tableName + " VALUES " + "('" + id + "','" + rname + "','" + rfn + "','" + rmn + "')";
Not related to the question, but strongly related to the proper creation of queries in Java:
You should avoid constructing queries with String contatenation. Instead, use PreparedStatement parameters. For example, you query would look like this:
strSQL="INSERT INTO " + tableName + " VALUES (?, ? , ? , ?)";

There is no field name specified.write like this
INSERT INTO tbl_name (col1,col2) VALUES(val1, vale2);
Check url:http://dev.mysql.com/doc/refman/5.6/en/insert.html

Java and Database Query?

Using Derby as my data base driver and tying to execute SQL query through java,
there was a error that was encounter, when tried to execute this particular query
stmt.executeQuery("insert into " + "TEST " + "values (" + dataTimeRev + ", "
+ dataType + "," + obj + ")" );
Here dataTimeRev, dataType and obj are variables with data.
The error that was stated was like this
java.sql.SQLSyntaxErrorException: VALUES clause must contain at least one element. Empty elements are not allowed.

if the column data type is VARCHAR you will have to pass the value in qoutes like 'value' for that you should do as below
String query = "insert into TEST values('"+dataTimeRev+"', '"+dataType+"','"+obj+"')";
stmt.executeQuery(query);

Verify that dataTimeRev, dataType and obj are not null and not blank.
I am not sure if Derby follows SQL syntax. But if the values are of type varchar, then it should be enclosed in single quotes ('). For example:
stmt.executeQuery("insert into " + "TEST " + "values ('" + dataTimeRev + " ', ' "
+ dataType + " ',' " + obj + " ')" );

Try this:
stmt.executeQuery("insert into TEST values ('" + dataTimeRev + "', "'+ dataType + "',"' + obj + "')" );

One of the causes of this error is trying to insert a Type that isn't a String (Date, Double, Integer e.t.c, surrounded by the single quotation mark ''
For example my table was declared like this:
String createTableStatement = "CREATE TABLE PRODUCT"+ "(product_id INTEGER NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1)," +
"product_name CHAR(80), "+
"price DOUBLE," +
"supplier CHAR(50))";
So I was doing:
statement.executeUpdate("INSERT INTO PRODUCT (PRODUCT_NAME, PRICE, DATE_SUPPLIED, QUANTITY, SUPPLIER) VALUES " +
"('" + productName + "', " + "'" + price + "', " + "'" + supplier +"')");
instead of:
statement.executeUpdate("INSERT INTO PRODUCT (PRODUCT_NAME, PRICE, DATE_SUPPLIED, QUANTITY, SUPPLIER) VALUES " +
"('" + productName + "', " + price + ", " + "'" + supplier +"')");