B.3 Differences Between PL/SQL and SQL Name Resolution Rules
PL/SQL and SQL name resolution rules are very similar. However:
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                     PL/SQL rules are less permissive than SQL rules. Because most SQL rules are context-sensitive, they recognize as legal more situations than PL/SQL rules do. 
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                     PL/SQL and SQL resolve qualified names differently. For example, when resolving the table name HR.JOBS:- 
                           PL/SQL searches first for packages, types, tables, and views named HRin the current schema, then for public synonyms, and finally for objects namedJOBSin theHRschema.
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                           SQL searches first for objects named JOBSin theHRschema, and then for packages, types, tables, and views namedHRin the current schema.
 
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To avoid problems caused by the few differences between PL/SQL and SQL name resolution rules, follow the recommendations in "Avoiding Inner Capture in SELECT and DML Statements".
Note:
When the PL/SQL compiler processes a static SQL statement, it sends that statement to the SQL subsystem, which uses SQL rules to resolve names in the statement. For details, see "Resolution of Names in Static SQL Statements".