Ms-access – Create new table values based on partial column value – access

ms accessnormalizationregex

I am trying to remove a ton of unnecessary rows in this table.

Currently there are 1.3m of them which are all an individual transaction id – with the country and destination assigned for each which is wayy wrong, given that the actual flight id is contained within the transaction id string.

The worst thing in the dataset which I've inherited, is the fact that within the transactions table there is a column with the extracted flight id as if it were a foreign key, but above is the 'flights' table. 'eyeroll'

My question is, how do I extract just the part which I have coloured in red? I can't use Left, Mid or Right, because they are variable lengths, some with 3 and 4 digits in the flight id itsself.

Is there a regex or something which can extract the text situated between 2 sets of underscores? which is just about the only viable rule in this sense.

Please bare in mind that I have never used regex before, and would need advice on how to format the expression in my query design view.

Any help is appreciated.

Best Answer

Since your starting position is fixed (after the 2nd _), you can use an Instr() function to find the position of the 3rd _, and just take the characters between.

Instr() returns the postion of the first instance of a character in a string. If the character is not found, it'll return 0. Note, Access considers the first character position to be 1.

Give this a try:

SELECT Mid(txn_id, 12, InStr(12, txn_id, '_')-12) 
FROM MyTable`

Just for reference: https://support.office.com/en-us/article/InStr-Function-85d3392c-3b1c-4232-bb18-77cd0cb8a55b

Edit:

This is pretty gross, but if the 2nd _ position was also variable, this should work:

SELECT Mid(txn_id
           , Instr(Instr(1, txn_id, '_')+1, txn_id, '_')+1
           , Instr(
                   Instr(
                         Instr(1, txn_id, '_')+1
                         , txn_id
                         , '_')+1
                   , txn_id
                   , '_')-1 -  Instr(Instr(1, txn_id, '_')+1, txn_id, '_')
            )
FROM MyTable

Firstly, a schema...

tblLocation(locationID[PK++], locationReference)
tblRoom(roomID[PK++], keyLocation[tblLocation.locationID], roomNumber)
tblRack(rackID[PK++], keyRoom[tblRoom.roomID], rackReference)
tblDevice(deviceID[pk++], keyRack[tblRack.rackID], positionU, deviceLabel)

...tables for custom devices can extend tblDevice

Foreign keys in square brackets, PK++ means an auto increment primary key.

As you can see, a Location has many Rooms, a Room has many Racks, a Rack has many Devices.

I have made primary keys as auto IDs as I prefer them to be integers and there's less to think about should you change a location/room/rack reference.

Populate this with Locations, Rooms and Racks as appropriate.

Solution 1 :: Not a lot of racks

Have three drop downs on the form.
User chooses a location, you then select all the rooms of that location in the next combobox.
User then selects the room, you then fill the next combobox with the racks in the room.
User then fills in device details and U position (which you probably want to validate to make sure that you don't have anything allocated there.)

Solution 2 :: Lots of racks

Have a query similar to:

SELECT
    rackID,
    locationReference + '-' + roomReference + '-' + rackReference AS [Full Location]
FROM tblLocation
    INNER JOIN tblRoom
        ON tblLocation.locationID = tblRoom.keyLocation
    INNER JOIN tblRack
        ON tblRoom.roomID = tblRack.keyRoom
ORDER BY
    locationReference ASC,
    roomNumber ASC,
    rackReference ASC

To generate a list of Location-Room-Rack references.

ABC-101-A/1
ABC-101-A/1
ABC-101-A/2
ABC-101-A/2
ABC-105-B8
ABC-105-B8
FAY-208-X8
FAY-210-A9T
FAY-210-A9T
FAY-210-F4
NAT-410-78
NAT-410-78

User selects one, then fills in the information. List will be equal to the number of racks (which could get a bit excessive).

Advantages

If you move a rack (or racks) of equipment from one room to another, it's just a simple update query to update the database
If a location/room/rack reference changes, you only have one piece of data to update.

Further schema additions

I've used racks in the past, I simplified the schema but these are some additions that spring to mind.

Add rackSize to tblRack: the size in U's
Add sizeU to tblDevice: the size of the device in U's

You can then do further validation: if you have a 39U rack and somebody tries to put a 5U device in at location 38, you can throw an error (as U's 40-42 don't exist!). Also if somebody puts a 3U device in at location 10, and something is in location 11, you know it won't fit or they have not updated the details of the device that is no longer there!

You could also make some clever queries that would tell you how much space there is in your racks (and where). But that's beyond the scope of this question!

Hope this helps.

Sql-server – How to split Date column values in Access into 2 columns

ALTER TABLE table ADD COLUMN Start_Date TEXT(6)
ALTER TABLE table ADD COLUMN End_Date TEXT(6)

update table
set Start_Date = Left(column,6),
End_Date = Right(column,6)