1 A Trio of Topics for Confident Access Query Writers ELSUG October 8, 2009 Cathy Salika CARLI

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A Trio of Topics for Confident Access Query Writers

ELSUGOctober 8, 2009

Cathy SalikaCARLI

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Three BIG Topics

Outer Joins

The BLOB Functions

Make Table Queries & Subqueries

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Outer Joins

Most sources call them “outer joins”.

Access calls them “left joins” and “right joins”.

The distinction turns out to be not very helpful, at least to me.

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Two reasons to use an outer join:

1) In case there are no matching data in a table you’re linking to

2) To find records that don’t have matching data in a table you’re linking to

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In case there are no data in a table you’re linking to...What could go wrong with this query?

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ITEMITEM_ID PRICE

1 $15.00

2 $180.69

ITEM_ID ITEM_BARCODE

1 309991234

3 309996789

ITEM_BARCODE

The normal join on ITEM_ID will give you just one record.

ITEM_ID PRICE ITEM_BARCODE

1 $15.00

309991234

Remember, you have to have matching ITEM_IDs in both tables to get a record.

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So what could go wrong with this query?

Items with no barcode will not appear.

MFHDs with no item will not appear.

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Think of some other examples where you might link to a table in which matching data might be missing.

A list of patrons, some of whom might not have barcodes

A list of purchase orders, some of which might not have invoices yet.

A list of items, some of which might not have statistical categories.

Others?

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ITEMITEM_ID PRICE

1 $15.00

2 $180.69


1 309991234

3 309996789

ITEM_BARCODE


1 $15.00 309991234

2 $180.69

<Null>

How do we fix this? We change the join.

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How’d she do that?

Right-click on the link...

... and select Join Properties

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You get this...

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Pick option 2, click OK, and the link turns into an arrow.

So what if I had picked option 3 instead?

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The arrow would be pointing the other way.

This is the “left” and “right” aspect of joining, but since this...

... is just the same as the picture above, I don’t find “left” and “right” very helpful.

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But it matters which table the arrow is pointing to!

A LOT!!!

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ITEMITEM_ID PRICE

1 $15.00

2 $180.69


1 309991234

3 309996789

ITEM_BARCODE


1 $15.00 309991234

2 $180.69

<Null>


1 $15.00 309991234

3 <Null> 309996789

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A list of items, some of which might not have statistical categories.

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Moral: All the links beyond the arrow have to be arrows too.

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A list of patrons, some of whom might not have barcodes

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Two reasons to use an outer join:

1) In case there are no matching data in a table you’re linking to

2) To find records that don’t have matching data in the table you’re linking to

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Suppose I want to find...

... the items that have no barcodes

... the bibs that have no holdings

... the patrons who have no barcodes

Use an outer join and check for the <Null> value.

The criterion is: Is Null

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Items with no barcodes

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Bibs with no holdings

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Patrons with no barcodes

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Any outer join questions?

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What can you do now that you couldn’t do before you learned about outer joins?

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Next topic: The BLOB Functions

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Voyager stores catalog data in two ways:

Frequently used data are in their own fields.

Things like TITLE, AUTHOR, DISPLAY_CALL_NO

Fields that need to be indexed

Fields in multi-bib displays

The whole MARC record is stored as a Binary Large OBject.

The BLOB functions let you get at any piece of a MARC record.

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The BLOB functions are indispensable, but they’re slow, so

Remember the Alternatives!

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Alternatives to the BLOB Queries

For common fields, try BIB_TEXT

For fields in left-anchored indexes, try BIB_INDEX

For fixed fields, try MARC*_VW (e.g. MARCBOOK_VW)

For URLs, try ELINK_INDEX

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BIB_TEXT p. 11, 14, 27, 33, 36The starred fields in this table are in UTF-8.If you need data from a bib record that are not available in BIB_TEXT, check to see if

they arein BIB_INDEX. Using BIB_INDEX and BIB_TEXT is more efficient than using the BLOB

functions.If you’re thinking of using begin_pub_date in a criterion, consider using the indexed

version of this field. It’s in the BIB_INDEX table, in the normal_heading field when

index_code=008D.<snip>Here’s how MARC tags map to fields in BIB_TEXT:Leader byte 5 record_statusLeader bytes 6-7 bib_formatLeader byte 17 encoding_level<snip>020 a isbn022 a issn024 a other_std_num027 a stdtech<snip>100 abcdkq author110 abcdgkn author111 acdegkn author245 abcfghknps title245 ab title_brief130 adfgklmnoprs uniform_title

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There are just 7 BLOB functions to learn

GetAuthBlob

GetBibBlob

GetMFHDBlob

GetField GetFieldAll GetFieldRaw

GetSubField

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GetAuthBlob(auth_id)

GetBibBlob(bib_id)

GetMFHDBlob(mfhd_id)

These three aren’t useful on their own. They ask Voyager for a MARC record. You use one of these as a building block for the other functions.

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Your query should include at least one table in which the ID field is unique, for example:

GetBibBlob([BIB_TEXT].[BIB_ID])

GetBibBlob([BIB_MASTER].[BIB_ID])

GetAuthBlob([AUTH_MASTER].[AUTH_ID])

GetMFHDBlob([MFHD_MASTER].[MFHD_ID])

BTW, capitalization doesn’t matter.

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You’ll wrap one of these

GetField

GetFieldAll

GetFieldRaw

around one of these

GetAuthBlob

GetBibBlob

GetMFHDBlob

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GetField gives you a single occurrence of a MARC field

Syntax:

GetField(

One of the Blob functions

,A MARC tag

, Which one? )

Example: the first 505 field in a bib record

GetField(GetBibBlob([BIB_TEXT].[BIB_ID]),’505’,1)

Example: the first subject (6xx field) in a bib record:


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Example: the first 505 field in a bib record


v. 1. Ancient Egypt through the Middle Ages -- v. 2. The Renaissance to the present.

Example: the first subject (6xx field) in a bib record:


Latin poetry, Medieval and modern History and criticism

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A Blob Function in a Query

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Using Shift-F2 to Zoom

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Zoom works with criteria too.

You can resize the font to improve readability.

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GetFieldAll gives you all occurrences of a MARC field

Syntax:

GetFieldAll(


,A MARC tag

)

Example: all of the 650 fields in a bib record

GetFieldAll(GetBibBlob([BIB_TEXT].[BIB_ID]),’650’)

Example: all of the 866s in a MFHD:

GetFieldAll(GetMFHDBlob([MFHD_ID]),’866’)

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Example: all of the 650 fields in a bib record

GetFieldAll(GetBibBlob([BIB_TEXT].[BIB_ID]),’650’)

Job enrichment

Employees' representation in management

Personnel management

You might have to make the rows in Access taller to see them all, because they all appear in one cell.

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Example: all of the 866s in a MFHD:

GetFieldAll(GetMFHDBlob([MFHD_MASTER].[MFHD_ID]),’866’)

0 no.1 (1958)-no. 6 (1962)

0 no. 8 (1964)-no. 11 (1966)

0 no. 16 (1968)-no. 18 (1973-1975)

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“Advanced Features” for GetField and GetFieldAll

You may add 2 more parameters to these functions

* a list of subfields that you want to see

* a separator to appear between subfields

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GetField(GetBibBlob([BIB_TEXT].[BIB_ID]),”650”)Forensic psychiatry Illinois Bloomington Case

studies.

Example: the first 650 field, subfields a and xGetField(GetBibBlob([BIB_TEXT].[BIB_ID]),”650”,1,”ax”)

Forensic psychiatry Case studies.

Example: the first 650 field, subfields a, x and z with double dashes between subfields

GetField(GetBibBlob([BIB_TEXT].[BIB_ID]),”650”,1,”axz”,”--”)

Forensic psychiatry--Case studies--Illinois--Bloomington.

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GetFieldRaw give you one occurrence of a MARC field, including the tag, indicators, and subfield coding.

* It’s the only way to get the indicators.

* It’s the only function that works with GetSubField.

Syntax:

GetFieldRaw(


,A MARC tag

Which one?

),

Example: the third 650 field in a bib record:

GetFieldRaw(GetBibBlob([BIB_TEXT].[BIB_ID]),’650’,3)

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Example: the third 650 field in a bib record:

GetFieldRaw(GetBibBlob([BIB_TEXT].[BIB_ID]),’650’,3)

650 0aDay care centersxGovernment policyzUnited States.

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245: getfieldraw(getbibblob([bib_text].[bib_id]),'245',1)

Ind1: Mid(getfieldraw(getbibblob([bib_text].[bib_id]),'245',1),4,1)


Use the Mid function to isolate the indicators.

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245: getfieldraw(getbibblob([bib_text].[bib_id]),'245',1)

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GetSubField gives you one occurrence of a MARC subfield.

You need GetFieldRaw and a Blob function with it.

Syntax:

GetSubField(GetFieldRaw(~etc~),

A MARC subfield code

, Which one?

)

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Example: The second $x from the first 650 in a bib record

GetSubField(GetFieldRaw(GetBibBlob([BIB_TEXT].[BIB_ID]),’650’,1),’x’,2)

Bibliography.

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The Blob functions can be slow, especially for large databases.

Avoid putting a criterion on a BLOB function.

Try to use the BLOB functions on a subset of your data.

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To sum up:

GetAuthBlob

GetBibBlob

GetMFHDBlob

GetField GetFieldAll GetFieldRaw

GetSubField

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Questions about the BLOB?

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What can you do now that you couldn’t do before you learned the BLOB?

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Make Table Queries and Subqueries: It’s an Art

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Make Table Queries and Subqueries fill the same need in different ways.

We’ll focus on Make Table Queries first.

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If you ever say to yourself...

“I know how to write this query, except that one of the tables I need doesn’t exist,”

...you need a Make Table Query.

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Example: List all the patron barcodes that appear more than once in my database and show who they’re assigned to.

It’d be pretty easy if you had this table, right?

Patron_Barcode Num_Occurrences

20999000012300

2

20999000076500

3

20999000034500

2

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So write a query that builds the table:

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To save the table in your Access database, you need to make it into a Make Table query:

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Then Access asks what the table should be called.

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I’ll call it

“Dup Patron Barcode Table”

Tip: You can’t have a table and a query with the same name. If you do, you get an obscure error message. To keep this from happening, I usually include “table” in my table names.

When the query completes, you’ll get this message:

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If you run the query a second time, Access will delete the results of the previous run, but it will ask you first:

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Now, when I look at the tables I have available...

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And when I open it…

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List all the patron barcodes that appear more than once in my database. That’s easy now!

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Another example: I want a list of the items that are both charged out and damaged.

That would be easy if I had a table listing the charged items and a table listing the damaged ones.

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A table of the charged items:

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A table of the damaged items:

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And a query to find the items in both:

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Another use for a Make Table query:

If you have a Blob query that you know will run for a long time, make it a Make Table query.

Start it before you leave work for the day.

I lock my workstation and tape a note to the power button saying that it’s locked.

With luck, in the morning, it will be ready to paste my results into the table.

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Make Table Query Subquery

Saves the results in your Access database

Doesn’t save the intermediate results

Makes your Access database get bigger

Doesn’t take up room in your Access database

It’s easy to look at the results before you go on to the next step.

You have to make a point of checking your results.

The results can be used by more than one query.

The subquery can be used by more than one query, but it is re-run each time.

Sometimes it’s handy to break up a long-running query into steps.

Sometimes it’s handy to run the whole thing in one step.

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Subquery example: patron barcodes that appear more than once in my database.

Write the subquery.

Don’t make it a Make Table query.

Don’t run it (except to examine and verify the results).

Save it.

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When I’m about to select the tables for the main query, click the Queries tab and select “Dup patron barcodes subquery”.

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Then click the Tables tab and select the other tables that you need.

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Add the links, save the query, and run it.

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Questions about Make Table queries and subqueries?

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What can you do now that you know about Subqueries and Make Table Queries?

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It’s been a whirlwind tour!

Thank you!

Documents

1 A Trio of Topics for Confident Access Query Writers ELSUG October 8, 2009 Cathy Salika CARLI