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A Trio of Topics for Confident Access Query Writers. ELSUG October 8, 2009 Cathy Salika CARLI. Three BIG Topics Outer Joins The BLOB Functions Make Table Queries & Subqueries.

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a trio of topics for confident access query writers
A Trio of Topics for Confident Access Query Writers

ELSUG

October 8, 2009

Cathy SalikaCARLI

slide3

Outer JoinsMost 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.

slide4

Two reasons to use an outer join:1) In case there are no matching data in a table you’re linking to2) To find records that don’t have matching data in a table you’re linking to

in case there are no data in a table you re linking to what could go wrong with this query
In case there are no data in a table you’re linking to...What could go wrong with this query?
slide6
ITEM

ITEM_BARCODE

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

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

so what could go wrong with this query
So what could go wrong with this query?

Items with no barcode will not appear.

MFHDs with no item will not appear.

slide8

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 barcodesA 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?

slide9
ITEM

How do we fix this?

We change the join.

ITEM_BARCODE

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

So what if I had picked option 3 instead?

the arrow would be pointing the other way
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.

slide15
ITEM

ITEM_BARCODE

slide19

Two reasons to use an outer join:1) In case there are no matching data in a table you’re linking to2) To find records that don’t have matching data in the table you’re linking to

slide20

Suppose I want to find...... the items that have no barcodes... the bibs that have no holdings... the patrons who have no barcodesUse an outer join and check for the <Null> value.The criterion is: Is Null

slide27

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.

slide29

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

slide30
BIB_TEXT p. 11, 14, 27, 33, 36

The 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 are

in 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_status

Leader bytes 6-7 bib_format

Leader byte 17 encoding_level

<snip>

020 a isbn

022 a issn

024 a other_std_num

027 a stdtech

<snip>

100 abcdkq author

110 abcdgkn author

111 acdegkn author

245 abcfghknps title

245 ab title_brief

130 adfgklmnoprs uniform_title

slide31

There are just 7 BLOB functions to learn

GetAuthBlob

GetBibBlob

GetMFHDBlob

GetField

GetFieldAll

GetFieldRaw

GetSubField

slide32

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.

slide33

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.

slide34

GetAuthBlob

GetBibBlob

GetMFHDBlob

You’ll wrap one of these

GetField

GetFieldAll

GetFieldRaw

around one of these

slide35

GetField gives you a single occurrence of a MARC field

Syntax:

One of the Blob functions

A MARC tag

Which one?

GetField(

,

,

)

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:

GetField(GetBibBlob([BIB_TEXT].[BIB_ID]),’6’,1)

slide36

Example: the first 505 field in a bib record

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

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:

GetField(GetBibBlob([BIB_TEXT].[BIB_ID]),’6’,1)

Latin poetry, Medieval and modern History and criticism

slide39

Zoom works with criteria too.

You can resize the font to improve readability.

slide40

GetFieldAll gives you all occurrences of a MARC field

Syntax:

One of the Blob functions

A MARC tag

GetFieldAll(

,

)

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’)

slide41

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.

slide42

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)

slide43

“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

slide44

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

Forensic psychiatry Illinois Bloomington Case studies.

Example: the first 650 field, subfields a and x

GetField(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.

slide45

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:

One of the Blob functions

A MARC tag

Which one?

)

GetFieldRaw(

,

,

Example: the third 650 field in a bib record:

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

slide46

Example: the third 650 field in a bib record:

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

650 0aDay care centersxGovernment policyzUnited States.

slide47

Use the Mid function to isolate the indicators.

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

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

Ind2: Mid(getfieldraw(getbibblob([bib_text].[bib_id]),\'245\',1),5,1)

slide48

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

Ind2: Mid(getfieldraw(getbibblob([bib_text].[bib_id]),\'245\',1),5,1)

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

slide49

GetSubField gives you one occurrence of a MARC subfield.

You need GetFieldRaw and a Blob function with it.

Syntax:

A MARC subfield code

Which one?

,

GetSubField(GetFieldRaw(~etc~),

)

slide50

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

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

Bibliography.

slide51

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.

slide52

To sum up:

GetAuthBlob

GetBibBlob

GetMFHDBlob

GetField

GetFieldAll

GetFieldRaw

GetSubField

slide56
Make Table Queries and Subqueries fill the same need in different ways. We’ll focus on Make Table Queries first.
slide57

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.

slide58

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?

slide62

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:

slide63
If you run the query a second time, Access will delete the results of the previous run, but it will ask you first:
slide67

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.

slide71

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.

slide73

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.

slide75
When I’m about to select the tables for the main query, click the Queries tab and select “Dup patron barcodes subquery”.
slide79
What can you do now that you know about

Subqueries and Make Table Queries?

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