what is a primary key  and foreign key constraints?
103863
Let's pretend we have a customer table with all our customers and an invoice table with all the invoices we've generated.  Each customer has a unique customer id, and every invoice has a unique invoice id PLUS has the id of the customer it belongs to.\n\nA primary key is usually used to make sure you don't have two records in the same table with the same key value.  If we had the same customer in our table twice, we might try to send them two bills, or do something twice.  The primary key constraint of uniqueness will not allow us to insert a second customer in the table with the same id.\n\nA foreign key is normally used to make sure the parent record IN ANOTHER TABLE exists.  For example, it would not make sense to create an invoice with no customer to send it to.  A foreign key constraint will not let you put a record in the invoice table unless the customer id on it exists in the customer table.
560387
Hello\nThere is some software that you can use , but I recommend ORACLE software they have a great database software with a great tutorial. \ngood luck there wonderful.
938312
INSERT INTO table_name (field1, field2, ...) VALUES ('value1','value2'...);
1054967
certain databases like mysql achieves this by using the dot operator "."\nsay db1 has table1(field1) and\ndb2 has table2(field2)then \n\nselect a.*,b.* from db1.table1 a,db2.table2 b where\na.field1 = b.field2
970593
You need to apply NORMALISATION. (Look it up if you need to)\n\nCreate a table for Status with 2 fields - one for text and one for an ID. Put in the different states (as listed in your question) in ascending order (think about this order carefully). Go to your original table, create a lookup field referring to the Status table. When building your query, now use the value of the ID field (e.g. StatusID>2)
252527
ok... i am guessing you are in some interactive query tool such as SQL Enterprise Manager (SQL Server) or Discoverer (Oracle). The problem is that your data isn't correctly normalized, and there are multiple rows that are equal (column A of row 1 matches column A of row 2, .... column n of row 1 matches column n of row 2). Your rows must be unique in order to use these tools to modify your data.\n\nHave you defined a primary key? If not, define one by adding a column (call it, maybe, PrimaryKey??) that is an "Identity" column in SQL Server, or a "sequence" in oracle. Then each row WILL be unique because the primary keys are unique.\n\nAre you viewing just a subset of the columns? In SQL Enterprise Manager, you can select the rows you wish to view by right-clicking on the table, then selecting OPEN, then selecting QUERY. If this is what you are doing, make sure to add your primary key to the query you're using to select and view the data. If you don't have a primary key, see the previous paragraph.\n\nIf this doesn't answer your question, email me.
772354
Even though the 'id' column is "NOT NULL" - you don't have to specify a default value if it has the special "auto_increment" option when you create the table.
409434
1. As a matter of fact, you should first see what is the exact relationship between tables. Maybe in some of them you need to create FK(foreign keys).You should create PK for every table but check first the things I've writhed earlier. Anyway, a table cannot contain 2 PK at the same time... so, I think you already have at least one tables who contains ENO and RPT_NAME at the same time... be careful. \n2. you can use a Stored Procedure to update your tables (not recommended).
967929
Best way is to have 2 tables.  A header and details table.\n\nThe header table will have one row per sale.  Key field would be invoice number.\n\nThe detail table will have details of each sale.  One row per item.  Key field would be invoice number and item number\n\nJoin field would be invoice number.
611776
In design mode, choose the field you want to have automatically populated (under Data Type column). Then click the "Lookup" tab (in the grey area below), and set the parameters in each field (use row source type Table/Query, and under Row Source, point to your other table).
436295
Database schema holds information, such as primary key, for the tables.
969293
http://www.databaseanswers.org/data_models/
1132129
Read this short review:\nhttp://en.wikipedia.org/wiki/DBMS
142385
Normalization is when you make a database not have redundant information. Technically, if you have a table of people and addresses, each state should be in a different table with a foreign key referring to it in the people table. For example:\n\nPeople\n-----------\npid - primary key int(10)\nname\naddress\ncity\nstateid - foreign key int(2)\nzip\n\nstates\n--------\nstateid - primary key int(2)\nstateabbrev\nstatelongname\n\nIn that way no single piece of data should be in the database more than once. But that's fifth normalization which might not make sense for what you're doing.
227264
fundamental of database designs - ramez elmasri & shamkant b. navathe
419239
I studied VHDL many years ago, but I cant remember for sure. I dont think you need a constraint file for every entity, only if it needs to meet tight constraints, like timing and such. \n\nSorry, cant be of much help.
340795
Hi,\nyou goto the table description properties.\nThe key which you want to make it unique and candadite..\n\nYou choose Primary key, meaning ... a key which cannot have duplicates.. like an id