SQL*Loader (sqlldr) loads data from external files into Oracle tables. The command sqlldr u1/oracle TABLE=emp uses defaults since no control file is specified. Let’s evaluate:
A. It overwrites the data for Alan and adds data for Curl and Bob.
Explanation:False. SQLLoader’s default mode is APPEND, not REPLACE. It doesn’t “overwrite” existing rows unless REPLACE or TRUNCATE is specified in a control file. Here, row 1, Alan, 2 exists, and SQLLoader will either skip it (if a primary key rejects duplicates) or raise an error, but it won’t overwrite. 3, Curl, 4 and 4, Bob, 4 are appended.
Mechanics:Without a control file, SQL*Loader assumes APPEND and matches columns positionally (ENO, ENAME, DN).
B. It generates a log that contains control file entries, which can be used with normal SQL*Loader operations.
Explanation:True. SQL*Loader always generates a log file (e.g., emp.log) when invoked. With no control file specified, it auto-generates one internally and logs it, including entries like LOAD DATA INFILE 'emp.dat' APPEND INTO TABLE emp FIELDS TERMINATED BY ',' (ENO, ENAME, DN). This can be reused.
Practical Use:The log’s control section is editable for future runs (e.g., changing to REPLACE).
C. It appends data from EMP.DAT to EMP.
Explanation:True. Default behavior without a control file is APPEND, adding new rows (3, Curl, 4 and 4, Bob, 4) to EMP. Existing rows (1, Alan, 2, 2, Ben, 2) remain unless constrained (e.g., unique key violations).
Mechanics:SQL*Loader processes each line of emp.dat, skipping duplicates if constrained, appending otherwise.
D. It generates a SQL script that it uses to load data from EMP.DAT to EMP.
Explanation:False. SQL*Loader doesn’t generate SQL scripts; it uses direct path or conventional path loading, not SQL scripts. The log contains control file syntax, not a script.
E. It overwrites all data in EMP with data from EMP.DAT.
Explanation:False. REPLACE or TRUNCATE would overwrite, but these require a control file with those options. Default APPEND preserves existing data.
