Question

I have several tables. I have a query also. My problem is to generate the SQL query dynamically using Java.

I have the following fields in a separate table:

 Collumn name          status
po_number,               Y
unit_cost,               Y
placed_date ,            Y
date_closed,             Y
scheduled_arrival_date   Y
date_closed              Y 
order_quantity           Y
roll_number              N
product_sku              N
product_category_name    N
rec_vendor_quantity      Y  
vendor_name              Y
et_conversion_unit_quantity Y

from which i have to generate a query when the status is Y, the problem here is some time the above columns

The following query is the out put of the above :

here i have inculded all the columns but i have to exculde the column which has the status of N, please help me to construt the query using java.

select
pi.po_number,poi.unit_cost,pi.placed_date CreateDate,
case when isnull(pi.date_closed) then pi.scheduled_arrival_date  
else pi.date_closed end as ReceviedDate,
poi.order_quantity,poi.roll_number,p.product_sku product_name,
pc.product_category_name,poi.rec_vendor_quantity,pv.vendor_name,p.et_conversion_unit_quantity,pi.note
from
purchase_order as pi,
purchase_order_inventory as poi,
product_vendors as pv,
products AS p,
product_categories AS pc
where
pi.purchase_order_id=poi.purchase_order_id and
pc.product_category_id=p.product_category_id and
poi.product_id = p.product_id and
poi.product_category_id=pc.product_category_id and
pi.vendor_id=pv.product_vendor_id and
( ( pi.date_closed  >= '2012-01-01' and pi.date_closed <='2012-09-05 23:59:59' ) 
or ( pi.scheduled_arrival_date  >= '2012-01-01' and pi.scheduled_arrival_date <='2012-09-05 23:59:59') ) and
pi.po_type=0 
and pi.status_id = 0 and  poi.transaction_type = 0  
order by pi.po_number 

UPDATE :

QUERY : STEP 1:

SELECT rcm.id,rcm.tablename,rcm.columnname,rcm.size,rcm.displayorder,rcm.isactive FROM report_customise_master rcm where rcm.tablename !='employee' and rcm.isactive='Y' order by rcm.displayorder;

STEP 2 :
Java method to construct the query :

public Map getComplexReportQuery() {
    String query = "SELECT rcm.id,rcm.tablename,rcm.columnname,rcm.size,rcm.displayorder,rcm.isactive FROM report_customise_master rcm where rcm.tablename !='employee' and rcm.isactive='Y' order by rcm.displayorder;";
    String tableName = "", from = "", select = "";
    StringBuffer sb = new StringBuffer();
    Map<String, List<String>> resultsMap = new LinkedHashMap<String, List<String>>();
    Map<String, String> displayOrderMap = new LinkedHashMap<String, String>();
    Map queryMap = new LinkedHashMap();
    if (!query.isEmpty() || query.length() > 0) {
        sb.append(query);
    }

    Connection connection = getConnection();
    if (connection != null) {
        try {
            PreparedStatement reportQueryPS = connection.prepareStatement(sb.toString());
            ResultSet reportQuery_rst = reportQueryPS.executeQuery();
            List<String> tables = new ArrayList<String>();;
            if (reportQuery_rst != null) {
                StringBuilder selectQuery = new StringBuilder(" SELECT ");
                StringBuilder fromQuery = new StringBuilder(" FROM ");
                while (reportQuery_rst.next()) {
                    tableName = reportQuery_rst.getString("tablename");
                    List<String> columns = resultsMap.get(tableName);
                    if (columns == null) {
                        columns = new ArrayList<String>();
                        resultsMap.put(tableName, columns);
                    }
                    columns = resultsMap.get(tableName);
                    String columnName = reportQuery_rst.getString("columnname");

                    columns.add(columnName);
                }
                tableName = "";
                for (Entry<String, List<String>> resultEntry : resultsMap.entrySet()) {
                    tableName = resultEntry.getKey();
                    List<String> columns = resultEntry.getValue();
                    int i = 0;
                    for (String column : columns) {
                        selectQuery.append(tableName + "." + column);
                        if (i != columns.size()) {
                            selectQuery.append(",");
                        } else {
                            selectQuery.append("");
                        }
                        i++;
                    }
                    if (!tables.contains(tableName)) {
                        tables.add(tableName);
                    }
                }
                //to remove comma at the end of line
                select = selectQuery.toString().replaceAll(",$", "");
                tableName = "";
                int i = 0;
                for (String table : tables) {
                    fromQuery.append(table);
                    fromQuery.append(" ");
                    fromQuery.append(table);
                    if (i != tables.size()) {
                        fromQuery.append(",");
                    } else {
                        fromQuery.append("");
                    }
                    i++;
                }
                from = fromQuery.toString().replaceAll(",$", "");
                queryMap.put("query", select + from);
            }
            //from = from+"ORDER BY "+orderbyColumn+" "+sort+" ";
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                closeConnection(connection, null, null);
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    } else {
        System.out.println("Connection not Established. Please Contact Vendor");
    }
    return queryMap;// return the map/ list which  contains query and sory and display order
}    

STEP 3 : Result query
{query= SELECT purchase_order.po_number,purchase_order.placed_date,purchase_order.date_closed,purchase_order.scheduled_arrival_date,purchase_order_inventory.unit_cost,purchase_order_inventory.order_quantity,purchase_order_inventory.roll_number,purchase_order_inventory.rec_vendor_quantity,products.product_sku,products.et_conversion_unit_quantity,product_categories.product_category_name ,product_vendors.vendor_name FROM purchase_order purchase_order,purchase_order_inventory purchase_order_inventory,products products,product_categories product_categories,product_vendors product_vendors}

but this not what i wanted, Please help me to construct the query i have given.

Answer 1

Two queries

You need to make two queries:

1. Query which fields are enabled
2. Build the second query string (the one you want to build dinamically)

It’s this way because a SQL query has to tell which columns will be included before querying any data. In fact it will be used to build the internal DB query plan, it is, the way the DB motor will use to retrieve and organize the data you ask.

Query all columns

Is it necesary to query only that fields? Can’t you query everything and use the relevant data?

Joins

Looking at the updated question I guess you need to dynamically add where conditions to join tables correctly. What I should do is have a reference telling me what coindition to add when a table is present.

There are at least two options:

1. Based on table pairs present (by example: “if A and B are present then add A.col1 = B.col2”)
2. Based on tables present (“if B is present, then add A.col1 = B.col2; A should be present”

Based on your example I think the second option is more suitable (and easy to implement).

So I should have some static Map<String, JoinInfo> where JoinInfo has at least:

JoinInfo
+ conditionToAdd // by example "A.col1 = B.col2"
+ dependsOnTable // by example "A" to indicate that A must be present when B is present

So you can use:

1. that info to add tables that should be (by example: even if A has no selected cols, must be present to join with B)
2. include the conditionToAdd to the where clause

Anyway… I think you are getting into much trouble. Why so dynamic?