Seagate ST43401N/ND Technické informace stáhnout pdf (Strana 69)

Migrating to Sybase Adaptive Server Enterprise 11.5 5-15

Adaptive Server Enterprise 11.5 If Your Current Version is 4.x

select columns from table1 t1, table1 t2

where clause ...

When used, correlation names must be used throughout the query.

For example, the following query is now invalid

select title_id from titles t

where titles.type = trad_cook

It must be rewritten as:

select title_id from titles t

where t.type = trad_cook

Mixing correlation names within subqueries, though not an error,

may bring different results:

select * from

my_table

where columnA =

select min(columnB) from

my_table

m where

my_table

.columnC = 10)

➤

Note

You should use explicit correlation names throughout your syntax. This

makes your applications easier to maintain. If you use explicit correlation

names in the from clause, use the same names in the select list and where

clause.

select into and NULL Column Headings

SQL Server 4.x allowed null column headings in tables created using

the

select into command. This can make SQL code and result sets

difﬁcult to read, and is not allowed under ANSI.

Versions 10 and 11 now require column headings to be valid SQL

identiﬁers.

Examples of select list items requiring column headings are:

• Aggregate functions such as

avg(advance)

• Arithmetic expressions such as column_name * 2

• String concatenation such as au_lname +, + au_fname

• Built-in functions such as

substring(au_lname,1,5)

• Constants such as results

Here are some syntax examples that specify column headings:

1 2 ... 64 65 66 67 68 69 70 71 72 73 74 ... 171 172

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Seagate ST43401N/ND Technické informace Strana 69